hi. i have a ravenheat boiler fitted 10 years ago.RSF820 been pretty good. had a leaking valve about two years ago and that was sorted very easily and cheaply but now causing over pressure/over heating problems. pressure actually goes above the limit and the overpressure valve operates and then when it cools down cos its lost water then needs topping up. hot water side works fine

mark juggins, October 2010

it most likely the expansion vessel. either it needs replacing as its got a hole in it or it needs inflating. its a vessel red in colour which contains a rubber balloon inside as the water in the heating system warms up it expands causing the balloon to shrink to stop the pipes or safety valve opening. what u need to do is drain the boiler of its water and open the prv valve or open a radiator nut know get on to the top of the boiler u see the tank behind it undo the black cap on top and inflate the tank with a car foot pump to 1.5 bar then close it. remember as u inflate to leave the rad or prv open as the water will push out the vessel. thats really it if it keeps need inflating then u need a vessel gl

kash, October 2010