I have a Baxi Combi instant 80he that looses pressure overnight. I have changed the pressure relief valve but it's made no difference. Is there anything else I could look at? All my pipes go through the loft and no leaks apparent and cant really afford a plumber to come out. Any help on what else could cause this would be great.
there's no air in the expansion vessel. it's behind the boiler. these boilers are not that well designed, the expansion vessel is too small and if you have 8 radiators or more (less than 8 if they're large) then you need an additional one.
to repressurise you need to open a drain point on the boiler when using a foot pump to pump it up to make sure you only pressurise the vessel not the whole system. access is over the top of the boiler.
the trouble with these boilers is the standard ex[ansion vessel has a store of hot water in it. you can fit an external one but if the standard one is packing up it's more than likely that the system required an additional vessel in the first place. standard ones only have a capacity of about 6 litres after you take away the space the store of the h/w takes up. go for a vessel 10 litres or more. 8 is the absolute minimum i'd fit.
it's lucky if the diaphragm separating the system water and air has gone. if it's the water store one that's split then it's definately a boiler off the wall job to replace the standard vessel, then add another vessel to stop if happening again. sounds like the water diaphragm is still fine though as that would constantly overpressurise and never drop.
I've got the original heating installer coming around tomorrow. He is going to fit an external tank which sounds ok. One plumber quoted £500 for two of them to do the job in 4 hours including removing the boiler from the wall. It worked out at about £50 an hour each !!! Not a chance.
The other plumber is fitting the external tank for fifty quid and I got the tank and inhibiter and connector for forty.
I hope this is the right way about this. Money wise it's alot cheaper, I just hope its ok in the long run as i'm not planning on moving.
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