Why does my glowworm 24ci keep over pressurising when heating is on?
The starting cold water pressure is filled to 1 bar and system is free from any air. Then the heating is turned on the pressure begins to rise. I realise that the pressure will do this slightly when the heating is on but this keeps on going until it gets to around 2.7 bar and then the prv starts to dump water. Surely it is not supposed to go up as much as this? The automatic air vent is open so believe that there is some fault with some sensor or some other part. Can anyone help?
Because the expansion vessel has lost pressure, the vessel cannot absorb the added pressure from the heating, thus causing the prv to open. The pressure then drops, you refill and it happens again. Isolate the flow and return to the boiler and depressurise the boiler. Then pump up the vessel to about 1.5 bar. Re open isolation valves. If prv is still dripping when pressure is less than 2 bar then also change this
Paulo B, December 2012
try venting the aav, little blck cap on top, loosen it, hopefully, you should loads of air out of it, failing that take ians advised
mac, December 2009
expansion vessel needs re-pressurised, also best to replace prv at same time.
