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Andrew Smith
Andrew Smith, Home Appliance Technician
Category: Appliance
Satisfied Customers: 3633
Experience:  Gas cooker specialist
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Worcester Greenstar 12i/24i boiler.

Customer Question

Worcester Greenstar 12i/24i boiler. Loss of pressure. No obvious leaks under the radiators. Pressure holds up on hot water but if CH has been on pressure drops back to zero. Builds up again when switched on with heating so pulling water from roof tank??


There is some water (dripping) from pressure release valve when boiler goes off. not a massive amount

Submitted: 4 years ago.
Category: Appliance
Expert:  Andrew Smith replied 4 years ago.

Andrew Smith :

The dripping from the pressure relief valve will be the problem.

Andrew Smith :

Are you able to see what pressure it will hold when you refill it?

JACUSTOMER-xkry49kp- : Once it has water in it will rise and hold on red (3) but as soon as the heating goes off it drops to zero. When water only on it holds at about 2 depending on what pressure has been put in at the start
Andrew Smith :

Ok, the PRV seems to be doing its job, but there is a problem with the expansion vessel

Andrew Smith :

Do you have a tyre pressure gauge?

JACUSTOMER-xkry49kp- :

Yes we do have a gauge

JACUSTOMER-xkry49kp- :

but how do we check the vessel with it please??

Andrew Smith :

If you empty the system, then look at the top of the boiler behind the frame, you should see the pressure gauge and the shraeder valve to check it

JACUSTOMER-xkry49kp- :

Do you mean we need to empty system completely?

Expert:  Andrew Smith replied 4 years ago.
Yes, or isolate the heating from the boiler underneath and open the PRV to drop the head and take the pressure gauge to zero