Thanks for the reply. As i am a complete noob when it comes to central heating where would I find a drain off??? sorry. Also I assume PRV = pressure relief valve.
thanks again
My central heating pressure keeps fluctuating. When switched off, the pressure sits at 1bar but when the CH is on, the pressure rises to 3 bar and is tripping the heating. It is a closed system with a flexcon Cubex expansion vessel. I was guided to try and re-pressurise this and have had no joy...