I have a ravenheat LS80T and when i don't use the Heating the pressure stays perfect but when I use the heating and the system goes cold after heating has switched of the pressure drops to zero thus stopping the boiler all together, I have changed the PRV but the pressure still drops and there are no leaks anywhere. all so the hot water temperature won't stabalise goes really hot then cuts out making it cold then cuts back in again, I have changed the DHW/CH potensiomiters which made no difference at all.

si689, November 2008

pressure vessel at back of boiler tee new expansion vessel into return pipe buy a vessel from screw fix 12ltr should do

damien, November 2008