My 20 year old oil fired boier for baseboard hot water heating system is building up excess pressure. I figured that the water inlet valve (manual, not auto-fill) was bad, thereby allowing curb pressure into the system, I replaced that valve. That did not solve the problem. I then turned my attention to air issues. I drained my expansion tank (old steel type) and it was not full. I installed new bleeders on all of the baseboard units and the bled as expected. I am confident that I do not have any airlocks.
I filled the system to 13# of pressure. It seems to work fine for a few days and then it creeps up to 25# or more. It has reached 30# and blown out of the PR valve. I've let water out several times to lower the pressure and somehow it seems to creep up again. Does anyone know of a possible source for this pressure increase? It's a closed system with no apparent leaks, well bled, and has a new water input valve. I cannot figure this out. Thanks. RNR