Pressure too low??

hi,
the problem is that when the water in the radiators heats up, it expands. if there is nowhere for it to expand to, then the pressure goes up so high that it discharges outside through the safety valve, then when the system cools down the water contracts again down to a pressure much lower than where it started.
so the fault here is that either there is too much water expanding for the boiler to cope with, or that the method the boiler uses to cope with the expansion is faulty.
in the former case it means you have too many radiators and need to add an expansion vessel into the syatem, or in the latter case you need to replace the expansion vessel in the boiler. in either case you need a heating engineer...

graham
January 2006