Combi boiler losing pressure but with a twist
Discussion
I have a Worcester Bosch condensing boiler fitted two and half years ago when I moved in. It is now losing all its pressure every time I turn the heating on or use the hot water after a while.
The boiler man says he checked the integrity of the boiler so it must be a leak in the pipes or joins in the house. I think it's the boiler and not the pipes in the house.
My query is that when we were away it did not lose any pressure. When I stop using the heating then it does not lose any pressure. But even if I just use the hot water it loses pressure after a couple of hours. And it's only got this bad now the weather has turned cold. When the weather was warmer it was not this bad.
Could this be due to something wrong with the boiler? Is there something I should be asking the boiler man to check (I'm a numpty with these things).
For reference, the house previously had a vented system. It was built in 1990 and has 10mm radiator pipes which are buried in the concrete floor and solid walls.
The boiler man says he checked the integrity of the boiler so it must be a leak in the pipes or joins in the house. I think it's the boiler and not the pipes in the house.
My query is that when we were away it did not lose any pressure. When I stop using the heating then it does not lose any pressure. But even if I just use the hot water it loses pressure after a couple of hours. And it's only got this bad now the weather has turned cold. When the weather was warmer it was not this bad.
Could this be due to something wrong with the boiler? Is there something I should be asking the boiler man to check (I'm a numpty with these things).
For reference, the house previously had a vented system. It was built in 1990 and has 10mm radiator pipes which are buried in the concrete floor and solid walls.
Countdown said:
I thought the same when my CH system was losing pressure (i.e. it MUST be the boiler as it only loses pressure when the boiler is running).
It turned out to be a leak under the floorboards in the hallway..
OK this doesn't sound good for me. I think I'm in this situation. We're talking over a litre of water top up each day at the moment in this cold weather. This has been going on for months but I cannot find any damp patches at all.It turned out to be a leak under the floorboards in the hallway..
leef44 said:
OK this doesn't sound good for me. I think I'm in this situation. We're talking over a litre of water top up each day at the moment in this cold weather. This has been going on for months but I cannot find any damp patches at all.
Mine was much worse. 2bar to empty in about 2 hours. In the end I had to get a specialist leak trace company out (which cost £700) and they only managed to get a rough idea where the leak was. Fortunately it turned out to be close enough and a plumber managed to pinpoint it and fix it. I gave him £250 because he managed to avoid damaging the laminate floor.
leef44 said:
The boiler man says he checked the integrity of the boiler so it must be a leak in the pipes or joins in the house.
I'm not sure why he'd think that with a combi as the primary water loop (to which the pressure gauge is connected and measuring) is entirely within the confines of the boiler when in hot water mode.Where does the condensate drain to? Can you access it? Whilst it will drip under normal operation I am wondering if there's a leak in the primary heat exchanger (i.e. inside the combustion chamber) and the leak water is passing out via the condensate drain hence not resulting in any other telltale signs.
A ‘boiler man’ should have checked this but just in case, try refilling the boiler and then watch the pressure gauge - it should rise as the water heats up then stay static, but if it keeps rising until it exceeds the maximum it will then open the pressure relief valve and release the water. If you can find the outlet for this valve - e.g. a copper pipe going outside - look to see if it’s dripping.
This combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
This combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
tux850 said:
leef44 said:
The boiler man says he checked the integrity of the boiler so it must be a leak in the pipes or joins in the house.
I'm not sure why he'd think that with a combi as the primary water loop (to which the pressure gauge is connected and measuring) is entirely within the confines of the boiler when in hot water mode.Where does the condensate drain to? Can you access it? Whilst it will drip under normal operation I am wondering if there's a leak in the primary heat exchanger (i.e. inside the combustion chamber) and the leak water is passing out via the condensate drain hence not resulting in any other telltale signs.
The condensate pipe goes to the ground outside and then below the concrete floor outside so difficult to check unless we disconnect the discharge pipe and collect the water.
My last house had a similar issue where I had to keep topping up but the condensate pipe was disconnected due to the frozen pipe outside. I was amazed how much water was coming out - several litres a day. Hence me thinking it is the boiler.
Countdown said:
leef44 said:
OK this doesn't sound good for me. I think I'm in this situation. We're talking over a litre of water top up each day at the moment in this cold weather. This has been going on for months but I cannot find any damp patches at all.
Mine was much worse. 2bar to empty in about 2 hours. In the end I had to get a specialist leak trace company out (which cost £700) and they only managed to get a rough idea where the leak was. Fortunately it turned out to be close enough and a plumber managed to pinpoint it and fix it. I gave him £250 because he managed to avoid damaging the laminate floor.
HalfManHalfJaffaCake said:
A ‘boiler man’ should have checked this but just in case, try refilling the boiler and then watch the pressure gauge - it should rise as the water heats up then stay static, but if it keeps rising until it exceeds the maximum it will then open the pressure relief valve and release the water. If you can find the outlet for this valve - e.g. a copper pipe going outside - look to see if it’s dripping.
This combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
This is what is up with mine, my plumber mate has recommended fitting the external expansion vessel to fix the problem. Mine has been faulty for a while but it’s only since the heating has been going on that I have needed to top up the system. I don’t think the pressure builds enough from just heating water, so the system hasn’t needed topped upThis combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
HalfManHalfJaffaCake said:
A ‘boiler man’ should have checked this but just in case, try refilling the boiler and then watch the pressure gauge - it should rise as the water heats up then stay static, but if it keeps rising until it exceeds the maximum it will then open the pressure relief valve and release the water. If you can find the outlet for this valve - e.g. a copper pipe going outside - look to see if it’s dripping.
Yes, I should've also said that I was assuming the boiler man has already checked the PRV outlet but of course shouldn't really make assumptions.J6542 said:
HalfManHalfJaffaCake said:
A ‘boiler man’ should have checked this but just in case, try refilling the boiler and then watch the pressure gauge - it should rise as the water heats up then stay static, but if it keeps rising until it exceeds the maximum it will then open the pressure relief valve and release the water. If you can find the outlet for this valve - e.g. a copper pipe going outside - look to see if it’s dripping.
This combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
This is what is up with mine, my plumber mate has recommended fitting the external expansion vessel to fix the problem. Mine has been faulty for a while but it’s only since the heating has been going on that I have needed to top up the system. I don’t think the pressure builds enough from just heating water, so the system hasn’t needed topped upThis combination of symptoms points to the expansion vessel - either faulty or with a leaking top-up valve (literally a car-type schrader valve). Not a big deal either way, easy to replace if there’s room to remove it with the boiler in situ, or it can be bypassed to an external expansion vessel.
Of course it could be a hidden leak slowly rotting your house from the inside out…..fingers crossed it isn’t!
When I told him about my old house boiler losing pressure he said that it was most likely the expansion vessel so this was one of the first things he looked at.
If its a slow leak you could try a chemical leak sealer
https://www.screwfix.com/p/fernox-f4-central-heati...
https://www.screwfix.com/p/fernox-f4-central-heati...
98elise said:
If its a slow leak you could try a chemical leak sealer
https://www.screwfix.com/p/fernox-f4-central-heati...
thank you, yes they did that during the summer and it did work for a while. It was losing 0.2 bar a day back then and this reduced it to 0.1 bar a day. So there was definitely a leak relating to the piping in the house but I'm wondering whether this is a red herring.https://www.screwfix.com/p/fernox-f4-central-heati...
Now with the much colder weather it seems to leak big time even when just using the hot water and not using the heating system. If both hot water and the heating system are not used then the boiler pressure remains stable for days.
Sounds like the expansion vessel has a split diaphragm.
Not using hot water won't affect it as the water has nowhere to go.
When the heating comes on it will pressurise and possibly open the PRV, therefore losing water again, if it gets that far.
As soon as you use hot water it will also bleed past the diaphragm and lose pressure.
Not using hot water won't affect it as the water has nowhere to go.
When the heating comes on it will pressurise and possibly open the PRV, therefore losing water again, if it gets that far.
As soon as you use hot water it will also bleed past the diaphragm and lose pressure.
BlackZeD said:
Sounds like the expansion vessel has a split diaphragm.
Not using hot water won't affect it as the water has nowhere to go.
When the heating comes on it will pressurise and possibly open the PRV, therefore losing water again, if it gets that far.
As soon as you use hot water it will also bleed past the diaphragm and lose pressure.
Although they did test the expansion vessel back in the summer, this is making me think it might be worth getting them to do the test again now for both the expansion vessel and the PRV. And this time to get them to walk me through it.Not using hot water won't affect it as the water has nowhere to go.
When the heating comes on it will pressurise and possibly open the PRV, therefore losing water again, if it gets that far.
As soon as you use hot water it will also bleed past the diaphragm and lose pressure.
Sounds like a leak in the pipe work within the concrete floor. A combi will operate under pressure hence it loses more water when heating is on, and less when off. We have this problem with ours although the pipes in the floor are mid-1970s when there was a common issue with copper pipes or unprotected pipes in screed.
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