Why is my central heating system over pressurising?
I woke up this morning to hear water running! on investigation I found that it was the pressure relief vlve on my central heating expansion tank letting off.
By this time the tank had drained to 0 bar so I re-set the valve and re-filled the tank to 2 bar and turned the water and heating back on. Within an hour the same thing had happened again, what is the problem? can someone please help?

Archie, December 2010

firstly 2 bar is too much pessure really it wants to be at about 1.5 when its cold this will creep up to about 2.1 bar when hot if pressure is still reaching 3 bar the expansion vessel has lost its charge and would need replacing as it allows for expansion in the pressure

aaron, December 2010