I fired up the coal boiler this afternoon. Everything was going fine till about 9:00 PM. The pressure relief valve opened on the oil boiler and wouldn't re seat ( water temp about 190 ). I shut down the coal boiler, shut down the oil boiler, and removed the relief valve after the system cooled. It had a rust- sludge build up in it so I thought this was the problem. Went to Home Cheapo, got a new one and installed it. When I fired up the oil boiler the new one relaesed at 140 deg. and won't reseat itself. Any thoughts? I've havn't had any problems with this system in the four years I've been using it.