Hi: I have a older Efm 520 boiler , I use it as a forced hot water system, the problem is when it is on a heating cycle it keeps building up too much pressure and tripping the pressure relief valve on top of the boiler. The boiler is a stoked that burnes coal. The pressure relief valve is pre-set at 30lbs, the system never ran that high before. What do you think the problem could be? The house uses the large standup radiators in the system, I also changed the expantion tank last year along with the water feeder valve. If you can help I would really appreciate it.
Thank you ottodog10