Mysterious pressure loss

[silberston]

Hi everyone,

I’m having some strange issues with my boiler that has our usual heating guy stumped and I’m hoping one of you friendly DIYers will be able to help.

It’s a Logic Combi 24 losing pressure, around 0.5 bar every 24 hours. I turned the boiler off and isolated the central heating feed and return and the pressure needle still fell. Connecting the heating back again, pressure rose. So seems conclusive it’s a problem with the boiler.

BUT, there’s no sign of water in or under the casing. The condensate pipe is completely dry when the boiler is off. A bag over the pressure relief outlet is also dry. Could be the expansion vessel but I recently put some leak sealer and extra inhibitor in the system and the pressure drop has slowed right down (but not gone away) – which makes me think it’s a leak rather than a problem with the vessel.

Tried ringing up Logic but they only give advice to registered gas engineers. Not sure where else to turn!

Any ideas? Thanks in advance

 

[ianmcd]

get the boiler hot and up to temp, then turn off, leave a few mins then check the condensate and see if it is dripping, sounds like a pinholed heat exchanger, if no water in the PRV outlet the expansion vessel is fine (note the PRV outlet would only drip after the heating had been on for about 30 mins or so) if the expansion vessel is faulty your system press gauge will be around 3 bar when the system is hot

 

[silberston]

Hi ianmcd, thanks for your reply. The heat exchanger is what I assumed but nothing came out of the condensate when I last left the boiler off all day. The system still lost pressure though. Would it only drip immediately after the system goes off?

 

[CBW]

Raise pressure to approx 2.7 bar and monitor.

Tried ringing up Logic but they only give advice to registered gas engineers.

Could your guy not try ringing Ideal?

 

[silberston]

Raise pressure to approx 2.7 bar and monitor.



Could your guy nit try ringing Ideal?

Good idea to raise the pressure higher. I'll give it a go.

He did ring Ideal himself, but from what he told me they didn't really have an answer beyond checking the PRV outlet and condensate. Only wanted to ring myself as I feel bad taking up more of his time!

 

[ianmcd]

Hi ianmcd, thanks for your reply. The heat exchanger is what I assumed but nothing came out of the condensate when I last left the boiler off all day. The system still lost pressure though. Would it only drip immediately after the system goes off?

sometimes they only leak when hot as the crack or pinhole expands when hot and the pressure inside the heat exchanger is greater when hot

 

[silberston]

sometimes they only leak when hot as the crack or pinhole expands when hot and the pressure inside the heat exchanger is greater when hot

Tried this last night but didn't see anything - but then the pressure didn't drop much so that obviously didn't help the test. I'll keep trying, and when I find a good time to have the heating off for a while, I'll try The Novice's suggestion of raising the pressure too.

Thanks again for your help!