In message , AJH
writes
On 17/11/2020 20:31, wrote:
I have a worcester bosch boiler, whose 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

new boiler? Apart from the pressure dial, the boiler is fine.



It's probably a failed expansion vessel

Certainly old enough.

Pressure vessels/system pressure has been exercising my mind lately
(never mind the just discovered manifold drip).

While the system was out of use, I checked the expansion vessel
pressure. Around 7.5psi but with a slight dribble of water. Pumped up to
around 1 bar.

Room temp to full system heat gives a pressure rise of around 0.8 bar so
within reasonable limits. However the slight drip has made me aware how
sensitive this set up is to system water volume changes.

My inclination is to reduce the expansion vessel pressure to say 0.8bar
(static head in a chalet bungalow not an issue) and the room temp.
system pressure to say 1.2 bar. This would use up some of the available
expansion volume but make the system more stable.

As has been said elsewhere before, I should really fit an additional
expansion vessel!

--
Tim Lamb