# Central Heating



## croft36 (6 Jan 2021)

Our old cast iron central heating boiler isn’t getting the water hot enough anymore! Can’t fathom out why! It runs continuously but the hot water outlet pipes to the radiators and the gravity fed storage tank only get moderately hot, they would usually get too hot to handle. As a consequence shower water not hot enough, radiators not effective. Any suggestions please?


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## D_W (6 Jan 2021)

do you know for sure that it's burning the same amount of gas or oil (whatever it normally would) when it's on? If it's oil, is there a chance that an injector is clogged?


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## porker (6 Jan 2021)

We had similar issues recently with our oil fired system which was a faulty 2 port valve. It only affected the heating but we have an S plan system which has 2 X 2 port valves. If yours is a Y plan system with a single 3 way valve it possibly could be that. Normally there is a lever on the valve to manually overide the motor. Worth checking that to see if it helps. Our symptom was the boiler continuously cycling and very little heat. New motor head fitted (didn't need to touch the plumbing at all) and it was fixed.


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## mikej460 (6 Jan 2021)

It sounds like you have a open vented system? If so you might have a problem with the header tank so pressure may have dropped. It could also be caused by a build up of rust scale in the boiler and/or pipes but check for water leaks under the boiler combustion chamber as the heat exchanger could have gone. How old is it?


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## Jos7000 (7 Jan 2021)

Older boilers have very little in the way of electronics, however, they do usually have two internal thermostats a high and a low. Perhaps one of those is in need of replacing. 
If so, you'll have to hunt online for them as older boiler spares are rarely found in part shops. My boiler is 30+ years old and I am solely responsible for sourcing parts as my gas engineer struggles with his suppliers. But it's not impossible, my only worry is when the heat exchanger gives up.


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## croft36 (7 Jan 2021)

Many thanks for all your replies. It is a 1960’s gas boiler, all the jets are clean and working and the flames have their usual appearance. The heat exchanger fins etc have been recently cleaned. The boiler thermostat is working but I have to turn it quite low before it switches burner off, at this point I can hear the pump running. I have now opened the boiler drain and after initial splurge of black and spurting across our breakfast room carpet (fortunately managed to clean carpet with soap and water before her indoors saw it!) the water appears clean but does actually have a few black particles in it. Basically I see it as a kettle full of water, switched on, but not heating the water as it should!. There are no electric valves in the system. I am now going to run it with pump not running ie gravity feed to hot water storage tank, towel rail in bathroom and one radiator only and see if boiler gets up to temperature?


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## Jos7000 (7 Jan 2021)

Have you checked the water pump is working?


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## Jos7000 (7 Jan 2021)

As in moving water, maybe the impellor fins have disintegrated


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## croft36 (7 Jan 2021)

Jos7000 said:


> Have you checked the water pump is working?


My thinking is that if pump wasn’t working the then stationary water in the boiler would get hotter. Also some radiators would not heat up at all. All our radiators are getting heat, just not enough. I just can’t weigh it up!


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## Glitch (7 Jan 2021)

Doesn't make sense. 
If it's on constantly then there is a lot of heat being generated. 
If the pump is failing then you'd see the boiler going on and off frequently as the boiler stat kicks in.
Outflow from boiler should be very hot unless the heat exchanger is clogged or scaled.
But if it's constantly fired up any water in the exchanger would be boiling.
Pump might sound like it's running but is it actually moving the water like it should. As Jos said the impellers might have failed.
But poor flow would mean boiler stat kicks in frequently...........

Sounds like you need a heating engineer


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## porker (7 Jan 2021)

Agree, if it were cycling constantly then that would make sense and would indicate poor flow but if running all the time then the heat would have to be going somewhere as it would boil the water as previously mentioned. If that were the case I would suspect the pump or scale and/or sludge. Is the pump external and does the pipe feel hot on the feed side? It should do and if not would show there is not enough flow. I've seen broken impellers on pumps so hearing it running does not necessarily mean it is pumping.


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## croft36 (7 Jan 2021)

mikej460 said:


> It sounds like you have a open vented system? If so you might have a problem with the header tank so pressure may have dropped. It could also be caused by a build up of rust scale in the boiler and/or pipes but check for water leaks under the boiler combustion chamber as the heat exchanger could have gone. How old is it?


No sign of water leaks.


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## mikej460 (7 Jan 2021)

croft36 said:


> No sign of water leaks.


ok so how old is the boiler?


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## nolly47 (7 Jan 2021)

Hi 
if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?


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## croft36 (7 Jan 2021)

mikej460 said:


> ok so how old is the boiler?


1960’s


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## croft36 (7 Jan 2021)

nolly47 said:


> Hi
> if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?


There is a hot water cylinder thermostat and room stat in the hall. Most of radiators have thermostatic valves.


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## Jos7000 (8 Jan 2021)

nolly47 said:


> Hi
> if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?


I'm not sure having the moneysworth out of an older boiler is relevant, it's more of a problem with modern tat that often becomes obsolete the second the warranty is up. Older boilers aren't plagued with the many issues their modern counterparts suffer from and if you factor in the cost of replacement parts and the engineer required to fit them, older boilers are no less economical to own.


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## HOJ (8 Jan 2021)

I would check the pump, been to loads of jobs where the impellers are clogged up with crud, so its pretty much just a spinning disc, still moving water, but without any force.


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## Glitch (8 Jan 2021)

Jos7000 said:


> I'm not sure having the moneysworth out of an older boiler is relevant, it's more of a problem with modern tat that often becomes obsolete the second the warranty is up. Older boilers aren't plagued with the many issues their modern counterparts suffer from and if you factor in the cost of replacement parts and the engineer required to fit them, older boilers are no less economical to own.



You have to consider running costs too. A modern condensing boiler is far more efficient between 14%-34% compared to a 30 year old one.
If your old boiler comes with high gas bills you might justify a swap. Plus you might get a grant towards a new one.

No question that modern ones are flimsy though.


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## Rorschach (8 Jan 2021)

Glitch said:


> You have to consider running costs too. A modern condensing boiler is far more efficient between 14%-34% compared to a 30 year old one.
> If your old boiler comes with high gas bills you might justify a swap. Plus you might get a grant towards a new one.
> 
> No question that modern ones are flimsy though.



Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.

An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.


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## Misterdog (8 Jan 2021)

Rorschach said:


> Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.



Only when in condensing mode though.
When they are not they are only 60/70 %.


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## Rorschach (8 Jan 2021)

Misterdog said:


> Only when in condensing mode though.
> When they are not they are only 60/70 %.



Well yes, but why wouldn't you use it in condensing mode?


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## Misterdog (8 Jan 2021)

You have no option, condensing mode is dependant on the system.
Something to do with the temperature differential on the flow and return pipes.
Just looked. my boiler has been on for 6045 hours of which only 57% was in condensing mode.



https://www.google.com/search?q=how+to+keep+boiler+in+condensing+mode&oq=how+to+keep+boiler+in+condensing+mode&aqs=chrome..69i57j69i64.18440j0j7&sourceid=chrome&ie=UTF-8



Strangely when selling you a new boiler they only focus on the 90% + 
figure.


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## Rorschach (8 Jan 2021)

Misterdog said:


> You have no option, condensing mode is dependant on the system.
> Something to do with the temperature differential on the flow and return pipes.
> Just looked. my boiler has been on for 6045 hours of which only 57% was in condensing mode.
> 
> ...



Sorry I thought you meant not have in on the condensing setting. Yes of course the boiler may not always work at full efficiency, but it's still going to way exceed a 60yr old boiler.


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## Misterdog (8 Jan 2021)

Indeed. There is no 'condensing setting' the boiler can only condense when certain conditions allow it to do so.
Though turning up the boiler stat reduces the time in condensing mode
(system dependant). I fitted weather compensation control which alters the stat automatically depending on the outside temperature.
I can tell how cold it is outside as the radiators get hotter.
The boiler has paid for itself in gas savings over 3 years, though I installed most of it myself.
It's an Ideal boiler which is superbly engineered, it has a processor and screen which gives me the information about burner time and efficiency level.
Far better than the Worcester Bosch I had before.


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## Rorschach (8 Jan 2021)

Misterdog said:


> Indeed. There is no 'condensing setting' the boiler can only condense when certain conditions allow it to do so.
> Though turning up the boiler stat reduces the time in condensing mode
> (system dependant). I fitted weather compensation control which alters the stat automatically depending on the outside temperature.
> I can tell how cold it is outside as the radiators get hotter.
> ...



On our ideal boiler there is a condensing setting for the temperature, it sets the water temp to 65c, the optimum condensing temperature. Of course I accept that this still may not mean it can work to full efficiency all the time.


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## Misterdog (8 Jan 2021)

Basically a boiler stat then, I suspect 65c would not be enough for my 160 year old house, especially as some of the radiators were installed in the 1970's.....


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## NormanB (8 Jan 2021)

Measuring the temperature difference at the feed pipe to the coil and the return from the coil at or towards the end of a cycle will tell you what is going on.

However, from what you have described the primary circuit is fouled and will require flushing, cleaning and inhibiting. This would also be a mandatory requirement prior to fitting a new boiler.

Given the age of the system AND if you live in a hard water area, the hot water side of the coil is likely to be heavily scaled. If that is the case the only practical/cost effective remedy is a new cylinder. So, a double whammy mitigating heat transfer on both sides of the coil.

If you know the history of the system - it is most unlikely the circulating pump is still doing the business - most will have given up the ghost at circa 20 years. Given the state of the primary circuit water adds grist to that mill.

However and all that being said. I have just looked at your photo again and there is no way the hot water cylinder is from the 1960s. I doubt judging by the energy label it is very old at all - when did those ‘labelling standards come in 2000+?

So that must shed some doubt on the age of the boiler I really doubt it’s is from the 60s’ - can you get make and model number serial number and do some googling. Likely to be similar age to cylinder methinks.


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## Glitch (8 Jan 2021)

Need the return temp at 55c or less to get it condensing. Too high a flow temp can make it less efficient as it returns higher than 55c.
Seems there is an art to tweaking condensing boilers for maximum efficiency. Most installers don't understand it, allegedly.
Also it seems most installers over-spec the power of replacement boilers - apparently that can work affect efficiency too. 

My Vaillant boiler was cycling too much when first installed. The replacement (energy efficient) pump wasn't man enough for the job so that got swapped for one with more grunt, plus the temp was reduced to 72c.
I'm reading on t'internet that 60c-65c is better. Going to try 65c and see what happens.
Also found the code (17) to enter installer mode. It gives you loads of additional data including return temp.


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## Misterdog (8 Jan 2021)

The bigger the radiators, or preferably underfloor heating, allow the return pipe temperature to be lower and hence in condensing mode more often.

Flow temperature - house heating 'loss' = return temperature. 

It's not as simple as turning the flow temperature/boiler thermostat down.
During really cold weather radiators need to run hotter to maintain a given room temperature.
One of the worst things people do, is turn up the boiler stat, in cold weather, and forget about it. 


Max Efficiency
For the condensing boiler to operate at maximum efficiency, the secondary heat exchanger’s surface needs to be equal to or below the dew point temperature of the fuel used. This is the temperature at which water droplets form. For natural gas boilers, the dew point is around 55C. In other words, the water in the return pipe needs to be 55C or lower or your boiler will not operate at maximum efficiency and potentially will not even condense.

Turning down the temperature on your boiler can help increase its efficiency. Most modern boilers will have a mark on the screen that shows you the point at which condensing mode will be turned on. For example, on Ideal Logic+ boilers, there’s an ‘E’ icon on the central heating dial, which is 68C.


There are factors that will affect this. For example, if you have smart heating with individual radiator valves, such as with the Honeywell Evohome, the return temperature can change. For example, if you’re heating the entire house, with all valves open, you’ll get a cooler return. If you’ve only got one radiator valve open, the return will be warmer.

However, the benefit of only heating a single room will mean that your boiler will shut down sooner, so the overall energy savings will be higher. For the best energy savings, a thermostat and boiler that can use OpenTherm will work best, as this lets the thermostat adjust (modulate) the water temperature for the best results.


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## Spectric (8 Jan 2021)

To get a condensing boiler to run in condensing mode the return temperature has to be low, around 55° C and to achieve this you must correctly size the radiators. Also they can be more efficient in newer instalations where full zoning has been applied through design, so all rooms can achieve the required temperature as they each control the boiler via a stat & zone valve. Gone are the days where there was just a stat and often the boiler just cycled.


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## Jos7000 (8 Jan 2021)

Spectric said:


> To get a condensing boiler to run in condensing mode the return temperature has to be low, around 55° C and to achieve this you must correctly size the radiators. Also they can be more efficient in newer instalations where full zoning has been applied through design, so all rooms can achieve the required temperature as they each control the boiler via a stat & zone valve. Gone are the days where there was just a stat and often the boiler just cycled.


Gone for the majority, but not everyone. 
My ideal elan, works just fine and I have no intention of scrapping it.


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## Spectric (8 Jan 2021)

I do believe you may have a pilot light!


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## Jos7000 (8 Jan 2021)

I do indeed, except in the warmer months following a high wind. I only use my boiler for heating, not for hot water. 
Standing charges mean I pay the same for a pilot light as I do for zero usage.


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## mikej460 (8 Jan 2021)

It does sound as if the system is clogged, which isn't surprising given its age. A word of warning that a professional flush is very expensive (I seem to recall paying £400 in 2006). Given the potential energy cost savings you might want to think hard about a replacement boiler, but investing in a visit and advice from a heating engineer would be wise. Our neighbour started to have problems with their old boiler and the engineer basically condemned it. They had a new energy efficient model fitted together with TRVs and halved their fuel cost in the first winter. They live in a 300 year old cottage.

This article might be helpful
Boiler Grants: Can I Get A Free Boiler? - Which?


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## Sandyn (8 Jan 2021)

If you want to try to hold on to your system, It's easy to flush out a central heating system. It's something you could do yourself. It may not give as good results as a power flush, but it will do enough to get it going again, assuming that is the problem. Will give you time to look at alternatives.


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## croft36 (8 Jan 2021)

D_W said:


> do you know for sure that it's burning the same amount of gas or oil (whatever it normally would) when it's on? If it's oil, is there a chance that an injector is clogged?


Gas consumption is the same as in 2019 when the boiler was performing as expected.


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## croft36 (8 Jan 2021)

Rorschach said:


> Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.
> 
> An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.


My boiler Crane Cavalial


Rorschach said:


> Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.
> 
> An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.


The boiler specification is input 80,000btu/h, output 60,000 btu/h which I took to equate to 75% efficient.


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## Jos7000 (8 Jan 2021)

mikej460 said:


> It does sound as if the system is clogged, which isn't surprising given its age. A word of warning that a professional flush is very expensive (I seem to recall paying £400 in 2006). Given the potential energy cost savings you might want to think hard about a replacement boiler, but investing in a visit and advice from a heating engineer would be wise. Our neighbour started to have problems with their old boiler and the engineer basically condemned it. They had a new energy efficient model fitted together with TRVs and halved their fuel cost in the first winter. They live in a 300 year old cottage.
> 
> This article might be helpful
> Boiler Grants: Can I Get A Free Boiler? - Which?


I'd be interested to know the actual figures in relation to expenditure for modernising, presuming their condemned boiler was very old. 
My point being, sometimes the outlay takes decades to recoup in fuel savings. Double glazing isn't always the investment people think and loft insulation can take twenty years if you have to pay for it. 
My system is open, modern pressurised systems would most likely require the replacement of the majority if not all of my system. Yes it would be cheaper to run, but at what cost to replace and maintain?! Modern boilers really can't last as long as much older versions and are often much less reliable.


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## Glitch (8 Jan 2021)

croft36 said:


> My boiler Crane Cavalial
> 
> The boiler specification is input 80,000btu/h, output 60,000 btu/h which I took to equate to 75% efficient.


It could now be the oldest working boiler in the U.K. 





__





42-year-old boiler stakes claim as oldest in the UK


42-year-old boiler stakes claim as oldest in the UK, Boiler and central heating installation and replacement, UK's leading directory of boiler and central heating installers. Get a quote from local boiler engineers at Boiler Guide.




www.boilerguide.co.uk


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## mikej460 (8 Jan 2021)

Jos7000 said:


> I'd be interested to know the actual figures in relation to expenditure for modernising, presuming their condemned boiler was very old.
> My point being, sometimes the outlay takes decades to recoup in fuel savings. Double glazing isn't always the investment people think and loft insulation can take twenty years if you have to pay for it.
> My system is open, modern pressurised systems would most likely require the replacement of the majority if not all of my system. Yes it would be cheaper to run, but at what cost to replace and maintain?! Modern boilers really can't last as long as much older versions and are often much less reliable.



Ah but we all have to go sometime, no matter how well we've performed in the past...

It really depends on the condition of your rads. If they're still ok but just need a flush then you might get away with you or the engineer/plumber removing them and flushing them outside. Converting to a sealed system is a straightforward re-piping job and removal of the header tank(s), we had this done at our last house.


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## Jos7000 (8 Jan 2021)

I'm quite proud of my old boiler and will do as much as I can to keep it going (I'm a believer in bangernomics), it's a very early copper exchanger model. I used to work in a national callcentre that covered utility insurance and the horror stories associated with modern equipment put me off for life. 
If it ain't broke... And if it is, fix it.


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## croft36 (9 Jan 2021)

Our boiler specification states input 80,000btu/h, output 60,000btu/h which I interpret as 75% efficient?


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## Jos7000 (9 Jan 2021)

Have you checked the pump efficiency yet? I swapped my pump as I bought a new one for £30, it changed my heating as previously cold radiators now get hot, the old one was still spinning up, just not working properly.


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## stevek (9 Jan 2021)

Were also running an old boiler, a Potterton Kingfisher, its an early one (30yrs plus as a guess) with a pilot light and cast iron heatexchanger, but its reliable and generally works fine and I really dont want to change it for a new boiler that friends and neighbours have found to their cost, are just plain unreliable, any savings in gas seem to be gobbled up by duff PCBs, callouts and fitters who often dont understand the bloody things themselves,,however our system is not the best, an 8mm microbore and now that this cold weather has arrived the system is struggleing and I wonder if this is the OPs problem? Were planning to keep going through the winter and see if we can give it an overhaul in the spring. The boiler is kettleing (bubbleing when running) so there will be sludge and scale in the boiler so my plan is to replace the pump, fit a magnaclean type filter on the return then run it for a few weeks with a system cleaner, then flush out as vigorously as we can with mains presure water. I doubt that it will be like new but Im hopfull it will improve matters.
Just as a matter of intrest, has the OP checked the flow and returns on the rads, Ive found hot flows and cold returns with rads barely warm,,somtimes a a blockage in the return pipe?


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## Spectric (9 Jan 2021)

The old pre condensing boilers with pilot lights did last a very long time, I have seen them over thirty years old and still going strong, albeit not super efficiently. Modern system boilers are generally more reliable than combi boilers, less complicated and work more leisurely. A combi to provide instant hot water goes through a lot of stress, rather like you being woken up with a bucket of cold water and then doing a long run. Well now they are looking to phase out gas boilers and make us all use electric or other sources, thats going to be very interesting. Everyone on electric heating with their electric car charging overnight, the old national grid will be groaning and adding to global warming.


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## Jos7000 (9 Jan 2021)

Spectric said:


> The old pre condensing boilers with pilot lights did last a very long time, I have seen them over thirty years old and still going strong, albeit not super efficiently. Modern system boilers are generally more reliable than combi boilers, less complicated and work more leisurely. A combi to provide instant hot water goes through a lot of stress, rather like you being woken up with a bucket of cold water and then doing a long run. Well now they are looking to phase out gas boilers and make us all use electric or other sources, thats going to be very interesting. Everyone on electric heating with their electric car charging overnight, the old national grid will be groaning and adding to global warming.


This is actually the only acceptable route for me, I have a full bank of solar panels (16 in total) they really do make a difference, I installed back in 2011 so I get maximum return on the investment, but my inverter packed in two years ago and was I surprised when the electric bill arrived! The only thing preventing me going electric for my heating is the extortionate cost of buying the stuff. Everything for me is down to value versus longevity and modern things really do not cut it compared to the cost.


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## Jos7000 (9 Jan 2021)

stevek said:


> Were also running an old boiler, a Potterton Kingfisher, its an early one (30yrs plus as a guess) with a pilot light and cast iron heatexchanger, but its reliable and generally works fine and I really dont want to change it for a new boiler that friends and neighbours have found to their cost, are just plain unreliable, any savings in gas seem to be gobbled up by duff PCBs, callouts and fitters who often dont understand the bloody things themselves,,however our system is not the best, an 8mm microbore and now that this cold weather has arrived the system is struggleing and I wonder if this is the OPs problem? Were planning to keep going through the winter and see if we can give it an overhaul in the spring. The boiler is kettleing (bubbleing when running) so there will be sludge and scale in the boiler so my plan is to replace the pump, fit a magnaclean type filter on the return then run it for a few weeks with a system cleaner, then flush out as vigorously as we can with mains presure water. I doubt that it will be like new but Im hopfull it will improve matters.
> Just as a matter of intrest, has the OP checked the flow and returns on the rads, Ive found hot flows and cold returns with rads barely warm,,somtimes a a blockage in the return pipe?


Take your radiators off one at a time and flush, shake, flush until you can't get any more crud out, flush the system after that leaving all the newly flushed radiators switched off to increase flow through the pipes. Be kind to your boiler though, if you blow the heat exchanger it will be game over for the boiler, unless you know someone who could fabricate a copy, preferably in copper.


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## stevek (9 Jan 2021)

Hi Jos,,electric is without doubt the future even without future legislation, we will look back on wet CH systems and wonder why we ever did it, my feeling is that you just pop along to Argos and buy a panel style convector heater, cost very little, no serviceing and if they go wrong you throw them away,,the only thing stopping us is the price of electric,,,I think there have been studies into the relative costs taking maintenence etc into account, and electric still comes out as more expensive,,however with a very well insulated house it might be different? Im assuming your high cost option is for storage heaters and using Off Peak electric?
Steve.


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## stevek (9 Jan 2021)

Jos7000 said:


> Take your radiators off one at a time and flush, shake, flush until you can't get any more crud out, flush the system after that leaving all the newly flushed radiators switched off to increase flow through the pipes. Be kind to your boiler though, if you blow the heat exchanger it will be game over for the boiler, unless you know someone who could fabricate a copy, preferably in copper.


Many thanks Jos, yep thats the general plan, anything to try and clear the rubbish out. If the boiler starts leaking were stuffed,,and it will have to be a new boiler, but it will be a sad day! Maybe there a new old stock Potterton laying around somewhere,,I should keep a eye on ebay!


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## Jos7000 (9 Jan 2021)

stevek said:


> Many thanks Jos, yep thats the general plan, anything to try and clear the rubbish out. If the boiler starts leaking were stuffed,,and it will have to be a new boiler, but it will be a sad day! Maybe there a new old stock Potterton laying around somewhere,,I should keep a eye on ebay!


You'd be lucky, at best keep an eye out for a decommissioned unit with intact exchanger. I've looked at mine and I doubt it would be too difficult for someone in the know to copy, they're not exactly special. A coil of pipe shaped to fit the boiler, with an alloy box to retain the heat and of course the fins. It's the pipes that bugga up, much of the rest could be recycled. Bearing in mind that mine isn't iron like yours. But the alloy box has the beginnings of a small vertical cracking which is being monitored. Luckily I know plenty of people with TIG welding setups.


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## sirocosm (9 Jan 2021)

I have an old Ideal classic with a cast iron exchanger, and a similar setup with a vented system and a vented cylinder (2 tanks in the loft), although my cylinder is not gravity fed. My system must be around 20 years old. I had a similar problem when I moved into the house, lukewarm rads, and lukewarm water. I took the head off the pump, and although it was working, the area around the impeller was full of crud, so I cleaned it out and it helped a bit. There was a thermostatic valve on the cylinder that was also seized so I took that out, which gave me hot water. Rads were still luke warm, so I took disconnected them one by one and used the hose to blow out blockages, which were not in the rads, but mostly in the microbore piping. After this I put in a jug of sludge remover and installed a magnetic filter. I could not believe how much sludge I emptied out of the filter over the next days, it was buckets. Over time all the rads, even the most distant ones are now working. I can only surmise that the previous owners did not use inhibitor, which I guess is essential for vented systems.

In my case when it was not working the boiler would not run very long, it would cut in and out. This is what I would expect if your system was blocked or the pump was weak. If the boiler is running continuously and the flow out of the boiler is still not getting hot, then I would suspect something wrong on the fire side.


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## stevek (9 Jan 2021)

sirocosm said:


> I have an old Ideal classic with a cast iron exchanger, and a similar setup with a vented system and a vented cylinder (2 tanks in the loft), although my cylinder is not gravity fed. My system must be around 20 years old. I had a similar problem when I moved into the house, lukewarm rads, and lukewarm water. I took the head off the pump, and although it was working, the area around the impeller was full of crud, so I cleaned it out and it helped a bit. There was a thermostatic valve on the cylinder that was also seized so I took that out, which gave me hot water. Rads were still luke warm, so I took disconnected them one by one and used the hose to blow out blockages, which were not in the rads, but mostly in the microbore piping. After this I put in a jug of sludge remover and installed a magnetic filter. I could not believe how much sludge I emptied out of the filter over the next days, it was buckets. Over time all the rads, even the most distant ones are now working. I can only surmise that the previous owners did not use inhibitor, which I guess is essential for vented systems.
> 
> In my case when it was not working the boiler would not run very long, it would cut in and out. This is what I would expect if your system was blocked or the pump was weak. If the boiler is running continuously and the flow out of the boiler is still not getting hot, then I would suspect something wrong on the fire side.


Yes thats an anomily with the OPs post, the boiler is fired up and running but not producing heat?? That seems to be an impossible situation!


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## Jos7000 (9 Jan 2021)

I wonder if the heat exchanger has come away from the pipes???


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## croft36 (11 Jan 2021)

Jos7000 said:


> Have you checked the pump efficiency yet? I swapped my pump as I bought a new one for £30, it changed my heating as previously cold radiators now get hot, the old one was still spinning up, just not working properly.


We have concluded that the pump is not spinning. We will be sorting that and see where we are then and will keep you posted.
One thing we overlooked mentioning is that there is a mixing valve at the pump inlet! I always thought that these were only used to moderate the temperature in the storage tank, this one only affects temperature in the radiators!? I wonder if I should remove it?


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## Jos7000 (11 Jan 2021)

I would leave that be.
It's a four way valve, I can't see how it's set, but they're designed to lower the temperature by mixing hot and cold together. 
Unless it's actually doing that, in which case I'd be thinking about changing the setting.


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## Glitch (11 Jan 2021)

They certainly don't make them like they used to!

Must have put it there for a reason but can't understand why you heat water in your boiler (using boiler stat to set temp) then cool it down by mixing it with cold water. Makes more sense for the hot water cylinder where you want the water a bit cooler. Maybe it's just belt and braces.

Can you switch between Hot water and heating, or is hot water always on if heating is on?


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## Jos7000 (11 Jan 2021)

Maybe the system has been altered in the past and it was just left in, perhaps the boiler was just overpowered when new. I believe underfloor heating can utilise lower temp heating.
I don't know anything about really old boilers, did they maybe not have internal stats and just keep belting out steaming hot lava??


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## croft36 (11 Jan 2021)

Jos7000 said:


> I would leave that be.
> It's a four way valve, I can't see how it's set, but they're designed to lower the temperature by mixing hot and cold together.
> Unless it's actually doing that, in which case I'd be thinking about changing the setting.


It was seized when we moved in 42 years ago!


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## croft36 (11 Jan 2021)

Glitch said:


> They certainly don't make them like they used to!
> 
> Must have put it there for a reason but can't understand why you heat water in your boiler (using boiler stat to set temp) then cool it down by mixing it with cold water. Makes more sense for the hot water cylinder where you want the water a bit cooler. Maybe it's just belt and braces.
> 
> Can you switch between Hot water and heating, or is hot water always on if heating is on?


Hot water is always on when Heating is on. The mixer valve only affects the heating water temperature. A pencil diagram of the system on the back of a circulating pump leaflet, presumably left by the plumber, indicates flows in the wrong direction in two instances, so he obviously knew what he was doing!!!!!


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## Glitch (11 Jan 2021)

So using logic (and no heating/plumbing experience whatsoever) I can't see the point of mixer valve for the radiators. Only makes sense for the hot water storage which needs to be cooler than the radiator circuit. 
Just use the boiler stat to set the radiator circuit temperature.

Is the pump itself knackered? I assume the wiring is live when called upon?


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## Jos7000 (11 Jan 2021)

croft36 said:


> It was seized when we moved in 42 years ago!


Is it actually a hot and a cold feed to the valve or has it just been repurposed?


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## Spectric (11 Jan 2021)

croft36 said:


> Hot water is always on when Heating is on.


Hi

If this is the case then how does the system prevent overheating of the sealed hotwater cylinder? The safety valve will let go at 100°C otherwise you would have bigger problems.


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## Glitch (11 Jan 2021)

Spectric said:


> Hi
> 
> If this is the case then how does the system prevent overheating of the sealed hotwater cylinder? The safety valve will let go at 100°C otherwise you would have bigger problems.



Presumably another thermostatic mixer valve.


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## stevek (11 Jan 2021)

I suspect its the same as was fitted to the Titanic or a left over bit of Doodlebug!,,,Ive done a fair bit of diy plumbing over the years and not seen one, but I would suspect that this was a way of regulating the hot water temp,,,in fact it has that old solid fuel look about it,,Its a pain but you could probably change over to a 3 port valve controled by a cylinder and room stats and programmer which I think would most likely save you a few bob too,,the trouble is if you cannot diy its how much a plumber would charge you,,touching the gadget itself is fraught with potential problems and I wouldn't be brave enough to do it,,


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## Spectric (11 Jan 2021)

I am always extra cautious with sealed systems, in particular ones that potentially contain stored energy and heating a large volume of water without full control can result in some bad outcomes. This system looks like is was one of the very first, probably before G3!


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## stevek (11 Jan 2021)

Is it a “sealed hot water cylinder”,,I very much doubt it?


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## stevek (11 Jan 2021)

Sorry for the multiple posts,,Ive just looked again at your photo and I think its a “Blending Valve” you can see the Red Dot hot feed and Blue Dot cold feed with the Red/blue blended hot and cold from the top and bottom tappings, on an old system the cylinder will be open vented and the cold feed for this valve will probably come from the cold water storage tank to balance the supply pressure, so its not regulating the cylinder temp, rather the temp of the water going to the taps,,,well thats my guess.
Btw you can still get blending valves and I think they might be mandatory in places like old peoples homes,,,


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## OldWood (12 Jan 2021)

Are blending valves not mandatory now for the taps in all modern builds ?


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## Jos7000 (15 Jan 2021)

stevek said:


> Hi Jos,,electric is without doubt the future even without future legislation, we will look back on wet CH systems and wonder why we ever did it, my feeling is that you just pop along to Argos and buy a panel style convector heater, cost very little, no serviceing and if they go wrong you throw them away,,the only thing stopping us is the price of electric,,,I think there have been studies into the relative costs taking maintenence etc into account, and electric still comes out as more expensive,,however with a very well insulated house it might be different? Im assuming your high cost option is for storage heaters and using Off Peak electric?
> Steve.


Sorry, only just saw this.
You are correct, storage heaters would be required as my electric is virtually free only while the sun is out.
All my lights are led to compensate for having to pay to turn them on.
I just wish the technology for harvesting rain energy was cheaper and easier to acquire, that said the feed in tariff wouldn't allow me to utilise it without reducing the amount they pay me. I would have to set up an entirely separate circuit. Bureaucratic nonsense!


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## croft36 (8 Feb 2022)

The hot water storage tank i


stevek said:


> Is it a “sealed hot water cylinder”,,I very much doubt it?


No it is vented. The hot water to the cylinder coil is not pumped.


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## woodieallen (10 Feb 2022)

I'd have been divorced by now if I hadn't sorted the problem out in over a year


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