Combi Boiler Pressure Keeps Dropping

[Robert Knight]

Hi. I have a combi boiler that keeps losing pressure and I have to top it up. I'm having to do this once a day. My local plumber says that it's the "expansion vessel". However, he said that if it was the expansion vessel then the pressure would shoot up when hot water was demanded but would then drop back. This does not happen I.E. the pressure does not shoot up when hot water is demanded it remains about the same as it was. The expansion vessel is inside the boiler and hard to access and he suggests a new boiler. The boiler is about 21 years old. What do people think? Could it be something more simple than the expansion vessel.

Thanks.

 

[Madrab]

2 things.

1) run the CH, once everything is hot see if the gauge has climbed up to 3 bar, if it has then yes it's the ~ EV. Then it needs its pre-charge checked and also check if the valve is passing system water. If it isn't passing water but there's no pressure then the EV just needs recharged, if it squirts lots of water then its internal membrane is burst.
2) If it is passing water through the valve then no you absolutely don't need a new boiler, you just need access to the return pipework to the boiler somewhere and tee in a remote expansion vessel.