Thanks for your reply. I assume you mean twist the plastic knob with 3 bar printed on it. I have done this many times. I have even given the valve a few swift taps with a hammer in the hope of freeing it.
The original problem was lockout due to overheating - air in the system.
I intend to...
When I attempt to repressurise the system water pours out of the overflow pipe outside. I think that this can only be a faulty pressure relief valve that is stuck open. Can anyone confirm this, or have other ideas?
Also can anyone recommend where I can get one of these valves. I tried the local...