DIY Doctor UK DIY Forums

central heating problem when heating is turned off the pressure is down to zero when i turn the heating back on i have to turn the pressure back up to for the heating to come back on then when the heating is up and running the pressure keeps on rising to about 3 bar which i know is double the normal the filling loop valve is fully turned off when topping up the pressure what could be the problem

When it reaches 3+ bar the PRV will open and water will be discharged via the PRV pipework to outside, the normal cause for this is that the expansion vessel diaphragm has stretched or split.

The expansion vessel needs re-pressurising or replacing. Press the schraeder valve to see if there's any air or water there.
Air - re-pressurise with a foot or hand pump to 1bar
Water - renew vessel.

htg