Strange plumbing issue

[MorrisWoodman12]

I've a strange problem with my plumbing so I thought I'd ask the vastly knowledgable collective for any ideas. Thanks in advance.

I live in a house built in 1970. Two years ago, after we moved in, the boiler was replaced along with removing the header tank, putting in a Thermstore hot water tank and generally updating everything to a sealed hotwater/central heating delivery system. Just about all the time we use an immersion heater to heat the water in the tank (about an hour each morning) and only use the boiler for central heating.

A few weeks ago we had the stop cock replaced as it was original and weeping. This increased the flow of water into the system as seen at all the taps. Last week we found the bottom of the boiler had water dripping from it and covering all the pipework and the floor. This was then repeated every night even though the boiler was off and occasionally we would look in the middle of the night and see it had occurred before the immersion heater turned on. Then a couple of nights ago I was awake and heard a sound almost mildly explosive in nature followed by a rushing water sound lasting about 4 seconds. This was repeated about a minute or two later. Water again is all over the boiler and pipework – it wasn’t an hour or so earlier. I found water dripping through a sight gauge (hope that’s the right term) and subsequently wrapped a towel around it. On two subsequent nights the towel has been wet and the floor and pipework remained dryish.

Before/above the sight gauge the pipe splits into two: one side to a temperature and pressure relief valve; the other back into the boiler.

We have also noticed the hot water is scaldingly hot since the problem started.

Does anyone have any ideas?

 

[Spectric]

A few weeks ago we had the stop cock replaced as it was original and weeping.

This may increase the flow but not the pressure, plus the cold water supply is not permanently connected to the boiler and is only used via the filling loop to pressurise the sealed part of the system.

What make & model of boiler ?

I would definately suggest that your best course of action is to get a heating engineer out because even if you find the problem you need someone "GasSafe" to repair it anyway and being a sealed system this is even more important and used to come under what was known as the G3 regs.

 

[brocher]

We had a similar boiler (a Viessmann) installed a few years ago, and it has a pressure vessel, and it also leaked. When I got the installer back out to look at it, they replaced the vessel. and then a couple of months later, the same again! So called them back and this time they spoke to the boiler makers about the problem, and it came down to the installers fitters being given the wrong training by the boiler maker! There ehsould have been a pressure relief valve installed when it was fitted! So all was sorted and no problems since. My installer who are very good reliable people, got compensation from Viesmann for all the problems they had caused them with the training!

So perhaps you are having a similar type problem?

 

[Sideways]

It sounds like a spring loaded temperature / pressure valve inside the boiler casing is venting to release excess pressure. That's the source of the water. Why it's venting is the more complex question and @Spectric 's advice is on the money. You need a professional to investigate and they need to be qualified to work on domestic boilers and G3 sealed heating / hot water systems so that they put it right.

Any of the following could cause or contribute to the problem you described, that's why you need a qualified plumber :

• Immersion heater
• Motorised valve(s)
• Hot water tank thermostat(s)
• Circulating pump
• Automatic bypass valve
• Expansion vessel
• Boiler controls

 

[MikeJhn]

I note there is no mention of an Expansion vessel, for sight gauge I assume the OP means the Tundish, is this drained to the outside or just free to discharge onto the floor?

Scalding hot water sounds like a temperature control valve/sensor malfunction witch explains the Tundish discharge due to the pressure relief valve opening because of excess expansion.

 

[Doug B]

I’m inclined to agree with MikeJhn, it sounds like your cylinder is over heating causing the excess volume of water caused by the over heating to be discharged through the tundish.
You need a G3 qualified plumber, one who is qualified to work on pressurised hot water cylinders, there will be a label on the cylinder which will have the original installers details if you don’t know another G3 plumber.
I’d also get the tundish looked at as it should if functioning correctly discharge to waste & not over the floor.

 

[Spectric]

Just about all the time we use an immersion heater to heat the water in the tank (about an hour each morning) and only use the boiler for central heating.

Last week we found the bottom of the boiler had water dripping from it and covering all the pipework and the floor.

and heard a sound almost mildly explosive in nature followed by a rushing water sound lasting about 4 seconds.

I think we can ignore the stop cock replacement and that it is just coincidence for the other issues.

The mildly explosive sound suggest the pressure relief on the cylinder opening to discharge excess pressure and this I would suggest is a secondary issue as your initial leak was from the underside of the boiler. Is the immersion heater wired correctly, it should be wired through a tank mounted thermostat and an over temperature switch also in the tank so in the event of a stat failure the O/T switch shuts off the immersion. For the immersion to cause an overheating issue would require a double fault unless there is a wiring issue that has now revealed itself because of a wiring issue and the thermostat has failed.

The boiler leak could be a separate issue but a system boiler is a very basic unit, just a boiler that heats water with none of the added complexity of the combi boiler with zone valves, expansion vessel & pump all being external so a leak would suggest a seal failure unless it is the condensing system, is the water just water or does it have a slight acidic taste ?


Either way @MorrisWoodman12 this is just information I am providing and being a sealed system I cannot emphasis enough the importance of getting a qualified heating enginneer out NOW and to NOT use the system until it has been inspected, a sealed vessel of water can create a huge pressure if heated to cause expansion without any capacity to expand into, simple law of physic's.

 

[MorrisWoodman12]

Thank you for all your replies so far. Some further comments. Being a retired electronics design engineer I like to understand the logic behind problems even though I don't necessarily have the knowledge to fix them. I'm sure lots of you occupy the same boat.
My heating engineer, who installed the boiler, tank and associated paraphernalia was coming yesterday but had eaten something Friday evening that disagreed with him: he's due Tuesday morning now.
The boiler is a Glow-worm Energy7 30S, the tank a Cyclone Plus by Joule. It is only connected to the mains via the filling loop. The two taps on this remain off unless a) the boiler pubescent pressure drops below ~0.7Bar. It's normally sitting at 0.9/1.0 bar cold. b) the fairies are mucking about at night.
The sight valve is indeed a tundish - just didn't know the right term & confirming things like that is what Google is good at. It has 15mm pipe in and >1m of 22mm pipe straight down into one side of the condensate pump. I think the mess over the floor is due to the initial force of the discharge. It's of such force that it covers the bottom of the boiler as well including much of the associated pipework. When I heard the discharge the other night it sounded like Push with an explosive 'P' followed by a rushing sound.

 

[MorrisWoodman12]

@Spectric Thanks for your latest reply. I don't think there is a leak from the boiler itself. After realising the tundish was 'operating' I loosely wrapped a towel around it. For two nights after that although the towel was wet in the morning the bottom of the boiler and all the pipework was dry.
I agree that the replacement stopcock is unconnected in all probability. Sounds logical anyway.
I'm pretty sure the only thermostat for the immersion heater is one of those ones that run centrally down the middle of the element itself. I don't think there is anything more complex than that. The overtemp cutout? I don't think there is one. I'll check later.
Yes there is an expansion vessel.
I'll try and get a reasonable photo of the system later although it's in a somewhat cramped space.
Martin

 

[Spectric]

It has 15mm pipe in and >1m of 22mm pipe straight down into one side of the condensate pump.

That sounds very wrong, look at diagram below. Items 2 & 5 are the over pressure / over temp valves that must be OEM fitted and part of the vessel. The pipe from these to the tundish under G3 regs, Pipe Min Ø equal to valve outlet and Max length between valve and Tundish 600mm. Pipe from the Tundish to point of discharge under G3 regs must be one size larger diameter than the pipe to the tundish, be vertical with no elbows for a min of 300mm, followed by a constant unrestricted fall. Connecting the discharge into the condensate pipe is a no no.

 

[Spectric]

The overtemp cutout? I don't think there is one. I'll check later.

This is a must have component, on my OSO cylinder it looks like this where the two switches are in series with the stat being adjustable and the over temperature switch has to be manually reset if triped.

Looking at Joule info you have one as part of the unit that looks like this ?

and the info states quote

"The immersion stat has an integrated high limit stat which If the primary thermostat fails the limit thermostat
takes over and shuts the element off before the water can boil in the cylinder."

This sounds like it removes a wiring issue and the immersion being the problem.

 

[MorrisWoodman12]

@spectre Thanks mate you are being a fantastic help.
Looking at the again this morning I noticed the hot water manual valve, after finding and downloading information about it, was in the manual position thus always open. Really don't know how that happened as neither SWMBO nor I have fiddled with it. The tank stat was up at 65C but shouldn't have been functional as the controller never commanded hot water. Have now set it to auto.
I attach a photo of the boiler cupboard. You can see the expansion vessel at the top. I'll also have a look at the immersion heater wiring to see how it can be combined with the over-temperature stat.

 

[MorrisWoodman12]

Can't sleep tonight!
Left boiler running last night but with the immersion heater turned off. I checked earlier that when it's turned off there's no power to it.
T&P relief valve released about 2;30am, twice as before.
Conclusion: although wiring to the immersion needs sorting out it has nothing to do with the problem.
Can't wait for the heating engineer to arrive tomorrow (Tuesday)
Martin

 

[Seascaper]

I've a strange problem with my plumbing so I thought I'd ask the vastly knowledgable collective for any ideas. Thanks in advance.

I live in a house built in 1970. Two years ago, after we moved in, the boiler was replaced along with removing the header tank, putting in a Thermstore hot water tank and generally updating everything to a sealed hotwater/central heating delivery system. Just about all the time we use an immersion heater to heat the water in the tank (about an hour each morning) and only use the boiler for central heating.

A few weeks ago we had the stop cock replaced as it was original and weeping. This increased the flow of water into the system as seen at all the taps. Last week we found the bottom of the boiler had water dripping from it and covering all the pipework and the floor. This was then repeated every night even though the boiler was off and occasionally we would look in the middle of the night and see it had occurred before the immersion heater turned on. Then a couple of nights ago I was awake and heard a sound almost mildly explosive in nature followed by a rushing water sound lasting about 4 seconds. This was repeated about a minute or two later. Water again is all over the boiler and pipework – it wasn’t an hour or so earlier. I found water dripping through a sight gauge (hope that’s the right term) and subsequently wrapped a towel around it. On two subsequent nights the towel has been wet and the floor and pipework remained dryish.

Before/above the sight gauge the pipe splits into two: one side to a temperature and pressure relief valve; the other back into the boiler.

We have also noticed the hot water is scaldingly hot since the problem started.

Does anyone have any ideas?

The most obvious is go back to the plumber who fitted the stop cock and find out if they knew what they were doing. There are an awful lot who have no idea what they are doing and cause a lot of damage often by not doing the job correctly or fitting wrong parts.

 

[Sideways]

In a system with a pressurised tank like yours, there should be two temperature/pressure relief valves. One is in the hot water side that flows through the boiler, radiators and the heating coil of the tank. This protects the system if the boiler heats the water too much / too long.
The second one protects the bulk water in the tank from expanding too much and bursting the tank if the heating (either the hot water coil or the immersion heater) gets stuck on and overheats the bulk, stored hot water.
Finally, there is a pressure regulating valve with a grey top on the pipe that supplies cold water into the tank before it gets heated. There is often an overpressure valve combined with that too.
Can you tell which of these three safety valves is the one that is releasing ? At least two if not all three of them will be piped to discharge through that grey tundish.

 

[Spectric]

It will be interesting to see what the heating guy finds on Tuesday.

Left boiler running last night but with the immersion heater turned off.

If you only had the boiler running for the central heating and no hotwater from immersion or boiler then the water release has to be due to the heating circuit UNLESS .

Now looking at your two zone valves, the one on the right is your hotwater cylinder coil and the one on the left is the single zone for the heating. On the top, cable entry side you will see a small metal lever in a slot, these should be loose and not in the latched position which holds the valve open. If for some reason the heating zone valve has been left fully open, (done whilst filling the system) then with the heating on the hotwater is also getting heated which would cause the pressure release.

If this is not the case then it will be down to the central heating circuit in which case you would have noticed a drop in the system pressure, if the pressure has not fallen then we are back to the hot water cylinder releasing excess pressure. For now just check those zone valves.

Here is what you will see, you want AUTO not MANUAL

 

[MorrisWoodman12]

@spectre Thanks mate you are being a fantastic help.
Looking at the again this morning I noticed the hot water manual valve, after finding and downloading information about it, was in the manual position thus always open. Really don't know how that happened as neither SWMBO nor I have fiddled with it.

Sorry just realised my post yesterday said hot water manual valve corrected by the auto spell check! Should read hot water motorised valve. So yes @Spectric both valves are now in the AUTO position. But even with them both in auto the problem still exists. I'm also fairly certain there has been no drop in system pressure - well certainly not a significant one.
Yes last night the immersion was off and the boiler hot water was off. The only heat source was the heating circuit.

 

[MorrisWoodman12]

In a system with a pressurised tank like yours, there should be two temperature/pressure relief valves. One is in the hot water side that flows through the boiler, radiators and the heating coil of the tank. This protects the system if the boiler heats the water too much / too long.
The second one protects the bulk water in the tank from expanding too much and bursting the tank if the heating (either the hot water coil or the immersion heater) gets stuck on and overheats the bulk, stored hot water.
Finally, there is a pressure regulating valve with a grey top on the pipe that supplies cold water into the tank before it gets heated. There is often an overpressure valve combined with that too.
Can you tell which of these three safety valves is the one that is releasing ? At least two if not all three of them will be piped to discharge through that grey tundish.

@Sideways Yes there is a pressure/temperature relief valve on the side of the hot water tank. The tundish also has a pipe going into the base of the boiler which I assume has a PT relief valve within it. As for a pressure regulator and relief valve on the incoming cold feed I assume it is the device pictured below. Please correct me if I'm wrong.
Martin

 

[Spectric]

The only heat source was the heating circuit.

So if the pressure has not dropped then we know the closed loop is not the issue, this means the issue is the hotwater cylinder releasing excess pressure. If this was occuring during it being heated by the immersion heater then we might suspect the expansion vessel but it seems to be happening when you are not asking for hotwater with the immersion. Either the boiler or the immersion must be heating the cylinder, there are no other means so what else could be wrong. Normally the expansion vessel for the cylinder is directly connected, with my OSO the pair of expansion vessels is built in under the top cover but looking at the Joule info it shows the expansion vessel 6 connected via that valve block, number 3 in the diagram. Could there be an issue with the valve 3.

 

[Doug B]

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

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