On 17/11/2020 21:08, AJH wrote:
On 17/11/2020 20:31, wrote:
I have a worcester bosch boiler, whoseÂ* pressure dial is all over the
place. Sometimes it's at close to zero in the red zone, sometimes it's
just in the green zone.

It's been behaving this way for many months.

Is this a problem with worcester bosch boilers in particular, or
boilers in general? When we get a British Gas engineer to fix it, he
increases the pressure so it's in the green zone. After a few weeks
it's fallen again into the red zone.

The boiler is ten years old. Can it be fixed? Should I be looking at a
new boiler? Apart from the pressure dial, the boiler is fine.



It's probably a failed expansion vessel

That would be my guess too, or perhaps it just needs topping up? Ever
since I had an old Vaillant getting on for 30 years ago where the vessel
was totally inaccessible, I have had an external one on my system.
Modern stuff seems to be much better designed for servicing.

If you are half handy with DIY, it may not be difficult to remove the
outer casing, then it is just a question of unscrewing the valve cap (if
water comes out, the diaphragm has failed), attaching a bicycle pump and
pumping it up to 20 psi or so (you will need to look that up). You
should be able to do all that without doing anything like disturbing gas
or opening the combustion chamber.

You imply that you never need to top it up. Also maybe worth taping a
clear polythene bag over the external overflow and checking after a few
days whether any water has come out.