Issue with Pressure in Heating System

kooper · 12-03-2021 11:14AM #1

I have issues with pressure in heating system, but I find it's behavior strange. I mean the pressure holds when system is not in a heating mode, it's ok when it's working, the pressure drop happens when the system is in cool down after working. Can anyone explain this behavior? One thing to mention, the service guy added 2 containers of sealer into the system and it still didn't helped.

Wearb · 12-03-2021 12:02PM

Did your service guy even have any idea where the leak might be?
Did he check the expansion vessel and pressure release valve?
What sort of heating do you have, radiators?
Gas, oil or/and stove?

It would be normal for pressure to drop when when cold and rise when hot.

kooper · 12-03-2021 12:24PM

I have gas heating system with 2 zones(potterton profile boiler).
Yes, I understand that with temperature drops the pressure might fall, but the behavior is systematic, and after going through heating cycle, the pressure drops and boiler goes E9 error on next attempt to start heating cycle as pressure is below expected . I'm not a specialist here so only cannot check it myself, but according to service man he checked the system(pressure valve, etc) and it's OK. We also tried to locate leak, using heat camera equipment, no luck there.
Currently I have one of those auto pressure input valves, that holds the pressure in the system, I let it work for a month now trying to see if any leak sign appears, but nothing so far. I understand that it most definitely a leak in the system, but the describe behavior keeps me thinking why the pressure doesn't go down when system is not on and during heating cycle but only after the system finished it's heating cycle and cools down.

I plan on contracting one of those firms that specialized on leak detection, but before doing so wanted to understand that behavior.

Wearb · 12-03-2021 12:52PM

There is a possibility that your leak is only happening when the boiler heats up due to system expansion. If inside the heat exchanger, it might be boiled off and evaporate through the flue or even through the condensate pipe. I don't do gas, so I wouldn't know if this is a possibility.

John.G · 12-03-2021 09:23PM

What is the system pressure when cold and then hot?

If you don't want to interfere/adjust the auto fill valve setting, just shut the isolating valve to it after pressurizing the system when cold and see does the pressure hold say overnight, if it does hold put the heating back on with the auto fill valve still isolated and carefully watch the pressure rise until fully hot, you may already have done all this anyhow.

kooper · 13-03-2021 11:49AM

When it's cold, the pressure is around 1, when system working it goes up to 2(~1.8-2). When we close auto valve the pressure holding as long as zone heating is off. When zone heating on, it holds all the way untill cooling down, and during cooling down it starts to fall. Also no presssure drop for heating water(without heating any zone), it drops only after zone heating was on.

Lenar3556 · 13-03-2021 12:04PM

kooper wrote: »

When it's cold, the pressure is around 1, when system working it goes up to 2(~1.8-2). When we close auto valve the pressure holding as long as zone heating is off. When zone heating on, it holds all the way untill cooling down, and during cooling down it starts to fall. Also no presssure drop for heating water(without heating any zone), it drops only after zone heating was on.

I would be looking at the expansion vessel - it may be undersized or defective.
You could also put a container under the outlet of the pressure release valve to see if water leaks from this at any point.

John.G · 13-03-2021 12:04PM

So. it drops below 1 bar with CH on and doesn't drop below 1 bar with HW only on?. (auto valve closed in both cases)

kooper · 13-03-2021 12:48PM

John.G wrote: »

So. it drops below 1 bar with CH on and doesn't drop below 1 bar with HW only on?. (auto valve closed in both cases)

It doesn't drop whenCH is on(steadily holds around 2), only when CH finished the cycle and system cooling down it goes almost to zero and boiler fails to start next time showing E9 error. With HW on it doesn't loose the pressure at all.

John.G · 13-03-2021 12:58PM

This is strange, if HW only on then I would expect the pressure to rise a little less than with the CH on, maybe up to 1.5ish but it should then fall back to 1 bar when boiler cools down, with the CH on I would expect the pressure to rise further to your 2 bar but obviously shouldn't fall below 1 bar when cold. Even if you never used the CH, all that system will be at the same pressure as with the HW on so if there is a CH leak then the pressure should still fall away to 0 bar IMO. if the expansion vessel is external to the boiler can you post a photo of it please.

kooper · 13-03-2021 01:30PM

John.G wrote: »

This is strange, if HW only on then I would expect the pressure to rise a little less than with the CH on, maybe up to 1.5ish but it should then fall back to 1 bar when boiler cools down, with the CH on I would expect the pressure to rise further to your 2 bar but obviously shouldn't fall below 1 bar when cold. Even if you never used the CH, all that system will be at the same pressure as with the HW on so if there is a CH leak then the pressure should still fall away to 0 bar IMO. if the expansion vessel is external to the boiler can you post a photo of it please.

Sorry for confussion about HW. When it's on the pressure goes up, but it returns back to 1 when off and it doesn't loose any pressure after(doesn't fall bellow 1).

Here is expansion vessel: boilerexpansionvessel.jpg(the spots there it's glue, not water).

John.G · 13-03-2021 02:07PM

Very mysterious, there is a pressure gauge under the magnetic filter, you may have another on the boiler, if so compare them making allowances for the elevation (height) between the two.

You should have a small 1/2" pipe coming off the boiler PRV and probably sticking out of the wall externally, it may be turned back into the wall, locate this and tape a small plastic bag around it and see if any water enters it with the CH on.

Lenar3556 already mentioned this.

Outkast_IRE · 13-03-2021 02:12PM

Safety valve passing a small amount when the pressure rises in the system ?

Wearb · 13-03-2021 02:27PM

Outkast_IRE wrote: »

Safety valve passing a small amount when the pressure rises in the system ?

He did say that service guy checked this, but who knows ðŸ€·

John.G · 13-03-2021 02:42PM

Yes, but worth self checking it with that bag?.

The only difference I can figure out between the HW & the CH is that the pressure should rise higher when the CH is on due to the larger volume but one wouldn't think that this should cause the fall to zero pressure on cool down except that the PRV is actually lifting which shouldn't happen until 3 bar.
Another bee in my bonnet is that there is no isol valve/combined drain to isolate the EV and check the precharge pressure without draining the whole system down, I think reflex make a nice neat one.
If the OPs precharge and filling pressure are the same then even the slightest leak will theoretically cause the water (boiler) side pressure to fall to zero as there is no reserve of 2/3 litres if the precharge/filling pressures are say 1/1.5 bar.

kooper · 13-03-2021 02:58PM

John.G wrote: »

You should have a small 1/2" pipe coming off the boiler PRV and probably sticking out of the wall externally, it may be turned back into the wall, locate this and tape a small plastic bag around it and see if any water enters it with the CH on.

Do you mean that white pipe, that goes into the wall, this pipe goes all the way to drain hole outside of the house? underboiler.jpg

John.G · 13-03-2021 05:25PM

I have the pipe from the PRV circled, I can't advise you how to access this (safety) you can figure it out yourself. What you can do is when the boiler is coming up to 2 bar pressure or whatever just feel this with your fingers, it should normally be cool but if the PRV is passing then will be quite hot.

kooper · 16-03-2021 11:00AM

John.G wrote: »

I have the pipe from the PRV circled, I can't advise you how to access this (safety) you can figure it out yourself. What you can do is when the boiler is coming up to 2 bar pressure or whatever just feel this with your fingers, it should normally be cool but if the PRV is passing then will be quite hot.

Did some experiments during weekend. The pipe there is not cold, but not very hot also, I'd say it's around 50-55C when CH is working. Also I've checked that white pipe output for water, taped a plastic bag to it. Today it poured around 300 ml of water there, Sunday only 50ml, and Saturday collected water twice from there 180ml each time. Does it mean that this is the issue with PRV and not the pipe leak?

John.G · 16-03-2021 12:03PM

The only certain way to check if the PRV is passing is to shut the boiler down, get that piece of pipe removed, pressurize the boiler to 2/2.3 bar and see if the PRV is leaking/passing., otherwise you don't know if the heat exchanger or the PRV is leaking/passing. The amounts of water you were getting, if the boiler was firing, could also have been normal condensate but that piece of pipe shouldn't be 55/60C IMO if not passing.

Outkast_IRE · 16-03-2021 03:51PM

kooper wrote: »

Did some experiments during weekend. The pipe there is not cold, but not very hot also, I'd say it's around 50-55C when CH is working. Also I've checked that white pipe output for water, taped a plastic bag to it. Today it poured around 300 ml of water there, Sunday only 50ml, and Saturday collected water twice from there 180ml each time. Does it mean that this is the issue with PRV and not the pipe leak?

That pipe has both the condensate pipe and the safety valve running to it , so by taping a bag to the end of it you could be getting condensate or water from the safety valve.

Issue with Pressure in Heating System

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