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Combi boiler is losing pressure but pressure increases on dial when firing.
I've been topping up by the filling loop, but the area under the boiler is now damp/wet.
Any ideas?
Plumber is coming tonight, but I thought I'd ask on here too 🙂
AFAIK there's a rubber bladder inside the steel tank of the expansion vessel. That's what fails then yes, can leak. I'm sure a gas safe engineer with actual knowledge will be along shortly to correct me. 😎
We had a boiler like that. Invested in a bucket and topped it up 3 times a week for a year and a half before complete heating rearrangement and new boiler. The most annoying thing was that it had been passed as OK when we moved in (nice shiny certificate) but didn't hold pressure for more than half an hour until I changed the filling loop. Plumber will likely either fix it or shake head and tell you it's new boiler time. Hopefully a few quid gets it straight again for you.
Could be the vessel it’s self leaking or the automatic air vent within the boiler. You’ll be loosing pressure out of the pressure relief valve sometimes they will reseal themselves after the vessel has been corrected sometimes not. If the vessel has gone and you’re getting pressure going right up to 3 bar ( the pressure limit for any domestic boiler then down to zero it’s not great on all the seals so it may just be a washer or an oring leaking.
What siflow says. Had the expansion vessel failed out just let pressure in the bladder over time? Your may just need to let assume water out, pump up the bladder with a bike pump, change the prv or even just clean the seat, and refill the system.
Ours failed last year and pissed out water.
Could be be linked might not, our expansion vessel loses air over time, just had to repressurise it. Conincidentally the boiler was also pissing itself last time it happened. Was even a leak, there was a hairline crack in the condensate flue which meant condensate was pouring out. Needs properly checking out.
The expansion vessel in our last boiler failed; when the heating came on and the pressure rose, water would escape from the pressure release valve down a pipe that went through the wall and then went I've no idea where as there was nothing on the other side! When the heating cooled down again the pressure would drop to too low, and I'd have to fill it up again and restart the cycle...
It was fixed by installing an external pressure vessel underneath the boiler.
Plumber came and suspects expansion vessel, but is sending someone else to properly diagnose. 🤞