Boiler losing pressure

[DB 16]

Hi all.

Would really appreciate some advice if possible, I have a valiant combi boiler and over the last couple of years it randomly seems to lose pressure,it will be fine today and then i'll go to put the heating or hot water on and nothing, i re-pressurised the boiler and all works fine, it can be run for months with no issues then it will happen again.

I have been through all radiators,valves, and trv's and there are no leaks which are visable, i had an engineer in about a year ago and he opened up the boiler pumped some air into the expansion vessel i think and everything seemed fine until it started doing it again over the last week, he said it was a common fault with these boilers.

My question is does this sound like something that the expansion vessel would do if faulty? i really dont want to start lifting the floor up looking for leaks so before i do i would like to hear what you guys think.

Thank you in advance

 

[steadyon]

1. If the expansion vessel is faulty, then, when the water is heated, the pressure will rise. If it reaches 3 bar, then the pressure relief valve will operate and dump water to outside. When the boiler cools it has no automatic way of replacing the dump water, so the pressure falls.
2. Check the point (normally outside) where the over pressure water is released. Usually a copper pipe "turned over" with fittings to point back against the wall. If there are signs of dripping, it is an expansion vessel / pressure relief valve issue. If no signs of dripping, tie a plastic bag over the end, and, the next time there is a problem, see if there is water in it.

 

[DB 16]

1. If the expansion vessel is faulty, then, when the water is heated, the pressure will rise. If it reaches 3 bar, then the pressure relief valve will operate and dump water to outside. When the boiler cools it has no automatic way of replacing the dump water, so the pressure falls.
2. Check the point (normally outside) where the over pressure water is released. Usually a copper pipe "turned over" with fittings to point back against the wall. If there are signs of dripping, it is an expansion vessel / pressure relief valve issue. If no signs of dripping, tie a plastic bag over the end, and, the next time there is a problem, see if there is water in it.

Thanks for the input, i will give that a try and see what happens, i know where the pipe is so i'll give it a try after and see if any water comes out.

 

[DB 16]

Just a quick update, so went to the boiler last night and there was no pressure so i topped it up and done as suggested and put a carrier bag around the copper outlet pipe and sealed it up. This morning tried to use the hot water and there was none so i knew that the pressure had dropped again, when i went and checked the bag there was a cup full of water inside the bag, so would that confirm that it is an expansion vessel/ Pressure relief valve issue?

Thanks in advance =)

 

[ShaunCorbs]

Yep time for a gas safe engy I’m afraid

 

[DB 16]

Yep time for a gas safe engy I’m afraid

100%, i would never touch anything gas related not worth the risk, i will be calling the engineer today, thanks for confirming that it is the PRV/EV

 

[centralheatking]

Just a quick update, so went to the boiler last night and there was no pressure so i topped it up and done as suggested and put a carrier bag around the copper outlet pipe and sealed it up. This morning tried to use the hot water and there was none so i knew that the pressure had dropped again, when i went and checked the bag there was a cup full of water inside the bag, so would that confirm that it is an expansion vessel/ Pressure relief valve issue?

Thanks in advance =)

You may find it cheaper to put an external expansion vessel in rather than go for a bespoke one
That’s certainly the problem the difference between 0 and 2 bar on a domestic system might only be
2 litre...the rest is in the exp. pipe. Chking

 

[moonlight]

Vaillant combi. Internal expansion. Easy fix for a qualified engineer.