Fluctuating boiler pressure

Kylo84

Hi everyone hoping for some help here.

Our Worcester bosch boiler (system not combi) has been acting funny. When the heating is off the pressure drops down to zero, and when I turn back on rises up to 1.5. i tried filling up to 1.5 when cold and turned on, and it jumped up to 3 so bled a radiator to get back down again.

Does anyone have any idead what might be causing this? Radiators seem to be heating up fine when the heating fires up so very confused!

Thanks

Ruski

Sounds like expansion vessel needs re-pressurising or has failed.

HTH

Russ

Kylo84

Is that the expansion valve in the boiler?

Ruski

It's not a valve as such - looks like a big balloon - normally red in colour, can't miss 'em

Russ

Ectophile

Look for a red cylindrical tank somewhere. They can vary in shape a bit, and are often tucked in the back of the boiler.

They are part-filled with air, for the water to expand into as it heats up. If they fail, they completely fill with water, so it's no longer got anywhere to expand into. As a result, the pressure shoots up as the system heats up.