The pressure in our gas boiler keeps rising. I've bled the radiators which brings it down temporarily. The top up valve is tightly closed so I can't figure out where the water is getting in.
Possible expansion vessel problem or it could just be a slight inlet off the cold supply to the heating system via the filling loop.
ADHS PLUMBING & HEATING
Expansion vessel in boiler, common problem.
It could be your exspaion vessel has lost its air and needs to be pumped back up. or there could be a split/pin hole in it.
Hi there could be a number of things , the expansion vessel could need charging or replacing
By law you are not allowed to remove the case from the boiler. the fault on this is inside the boiler so you need somone who is gas safe sorry.