Strange plumbing issue

[Spectric]

But why would a faulty valve 3 the pressure reducing valve cause the water to be scalding hot & why only discharge at night

A very good question, expansion vessels are a common cause of pressure release from cylinders but not just at night !

Scalding hot points back to the thermostat but hot water was off so we have an unknown reason for the heating, at night you don't have hot water usage so during the day you are keeping the pressure down by using water, at night no usage and pressure builds up, almost as if there is some path between the central heating and hot water circuits.

 

[MorrisWoodman12]

I can almost theorise a solution to the night release. We've had a) the stopcock replaced along with some very minor rerouting of the cold feed pipes and b) a new housing development being connected to the mains supplies recently a few hundred yards down the road. If some muck has got past the filter then the regulator could be playing up. If the water pressure increases overnight then that could cause the release. Also note that since the stopcock has been replaced the hot and cold water flows have increased.

I can't explain the scalding hot water. I ran a tap yesterday and stuck a thermometer into the flow. It topped out at 65C. Currently the boiler is on programmed for heating. The entry and exit at the tank for the coil are both cold. The immersion has been off for at least 24 hours now. We are not consciously heating the hot water at the moment to see if it is gaining heat from anywhere else.

 

[Doug B]

Martin is your boiler on an outside wall & does the balanced flue go out of the back of the boiler through the wall?

 

[MorrisWoodman12]

Doug. Hi!
No it's on an inside wall so the glue goes vertically up and out through the roof.

 

[Doug B]

Well that shoots that train of thought out of the water.
I very much doubt the stopcock change will have any bearing on your problems, there’s a very fine mesh filter in the inlet to the pressure reducing valve which would be more likely to reduce flow if detritus had collected in it.

 

[Spectric]

Currently the boiler is on programmed for heating.

That made me think that although you have a system boiler it sounds a little more than a "system boiler" so this is the diagram for the 30S which shows a pump and expansion vessel for the heating. I find the idea of the expansion vessel a little odd as they are sized to suit the volume of the heating system, ie number and size of rads so can only assume that you might be expected to fit extra expansion capacity if needed. Normally a system boiler is just that, a boiler where everything else is external. The manual for these boilers is not great so another possibility is a wiring issue or setup as it is far more complex than a bare bones system boiler.

 

[MorrisWoodman12]

Roy. Hi!
Don't know what to think about your latest suggestions i.e. a wiring or setup issue but would ask why it has only happened since the stopcock has been changed. If it was wiring or setup then surely it would have been like it from the get go.
Engineer due tomorrow thank goodness.
Best regards
Martin

 

[MorrisWoodman12]

PS. There seems to be more on the 'watch notice' emailed than on the post above. Strange. Anyway in answer to your question "Just checking, what do you have for the controller, a combined heating / hotwater or seperate controllers ?" it's a combined heating/hotwater controller. A Honeywell ST9400C.

 

[HOJ]

Bit of a ramble, I still dabble in a bit of plumbing, (was a qualified G3 unvented installer, up until the thieving scheme organisers decided the "life time" ticket needed updating every 5 years and a new subscription scheme paid for, but there weren't any updates..so I'm not anymore.)

Any way this could well be an incidental issue making a bigger one, my view, the stop cock change out has probably increased the system pressure, as it was probably throttling the pressure back before, and now the greater flow rate, only way to check is to put a pressure gauge on it, (which we used to do before installation to make sure there was at least the minimum needed for an Unvented system to work, and record it on the commissioning paperwork) therefore consequently the higher pressure and flow rate may have exposed a dormant fault.

We used to find that the incoming mains water pressure, overnight, could well go from 2 to 7 bar+.

As an aside I was out on a call out yesterday for an UFH fault, not one of my jobs, client had been told the motorised valve wasn't opening and needed replacing but "plumber" couldn't come back till next week to fix it, client bought a new Honeywell 2 port valve, the symptom was right, but having dropped the system out, replaced the vale and refilled, the flow pipe still didn't get hot, next thing in line was a ball valve, got into that and water flowed freely, next thing was the
mixer/blending valve, a bit like a gate valve, undid that, nada, spindle shaft came out but the plastic cage in the valve was stuck in at the back, it is spring loaded so should have popped out, gave it a tug, ping, it released, put it all back together, refilled the system, heating came up, that took 31/2 hours.

Moral of my tale is it isn't always the logical thing that's is the problem, be interesting to know the engineers diagnosis.

 

[Spectric]

but would ask why it has only happened since the stopcock has been changed.

The stop cock might just be a red herring, yes if the old one was partially seized and not fully open then it would effect the flow rate but not the pressure so now you may have more flow but I cannot make a link with the water getting much hotter and the excess causing over pressure.

it's a combined heating/hotwater controller. A Honeywell

I was curious as to what you said about

Currently the boiler is on programmed for heating.

That suggest the controls were on the boiler and normally they are remote.

well all will be revealed tommorow !

 

[Stevekane]

Always find plumbing questions very interesting, and Ive no real experience of sealed systems, but a couple of thoughts, is the water discharging really scalding hot,,hot water feels very hot anyway and might even burn you? and the coincidence of the stopcock,,is it possible that your expansion vessel needs pressurising,,I think presurised H/W cylinders have these? mains water pressure can increase at night and I think that in your system the discharge into the Tundish is of your domestic hot water, not the heating circuit,,so its at Mains Pressure,,,back to that stopcock coincidence?

 

[Spectric]

so its at Mains Pressure,,,back to that stopcock coincidence?

But there is a pressure regulator that maintains a constant lower pressure on the hot water vessel infeed so any fluctuations with the mains should not be seen with the hot water pressure.

 

[Stevekane]

But there is a pressure regulator that maintains a constant lower pressure on the hot water vessel infeed so any fluctuations with the mains should not be seen with the hot water pressure.

Good point,, but our friend has said that the discharge is occurring when neither the heating system or the immersion are on,,,a static system is discharging (only?) due to an increase in pressure from where?
Its very perplexing. BTW Im aware that the stopcock would only affect the flow of water and not the pressure,,,so all the more confused. Just a thought, why not turn off the stopcock before “retiring” and see if the discharge still occours?

 

[Spectric]

why not turn off the stopcock before “retiring” and see if the discharge still occours?

A good idea, you now have no external input to the hot water vessel and unless hotwater is used you have a constant pressure in the vessel so without any heat source there can be no rise in pressure that would result in a release. We are also looking at the volume increase due to the expansion of water that is exceeding the volume of the expansion vessel unless the diapragm has a hole and so again to reach the point of release requires both no hotwater use and time to build up.

 

[MorrisWoodman12]

Progress – yet to be proven

Engineer here at 9AM. Incoming mains water pressure at 10AM 6 bar but in all likely much higher late at night when there is little water usage.

Pressure regulator on incoming mains to hot water at factory setting of 3 bar but was letting through as it had muck in the valve. I don’t know where the muck came from as there is a filter in the regulator inlet. Thus it was letting the higher night pressure through which was being released by the over-pressure relief valve releasing a spray of water from the tundish.

The condensate pump has been removed so the tundish outlet is now a plastic pipe (32mm?) going externally and will have a lime sump to nullify the acidic condensate. Future job as no stock locally but should be available to fit Saturday.

The tundish supplied with the Joule Cyclone Plus hot water tank will also be replaced with a transparent but fully enclosed one so no water escapes.

So tonight I’ll have the system running as ‘normal’ i.e. heating on, though obviously off at night, and the immersion heater on between 6 and 7AM. We’ll see what happens and report back.

 

[Spectric]

The condensate pump has been removed so the tundish outlet is now a plastic pipe (32mm?) going externally and will have a lime sump to nullify the acidic condensate.

Don't get to concerned about the acidity of the condensate, it is more akin to tomato ketchup than something that removes paint or skin. Fill the sump with lime chippings as they neutralise any acidity. The tundish is for release from the safety valves, the condensate is run independant without a tundish because the condensate is supposed to flow whilst you need a means to see if the safety valves have been letting through. So ideally the outlet from the tundish should be free flow without restriction, ie not into a condensate sump but I have seen it done but with the condensate piped in below the tundish.

Lets hope you have no more issues and a good nights sleep, your mains pressure is high so maybe another job in the future is to fit a pressure regulator just after your main stop cock. These issues are often as a result of building large housing estates without any thought given to the services.