My boiler had sprung a leak last year and I got it welded. This spring it began to leak again. I've since discovered that the pressure gauge and pressure relief valve needed replacing. I've got both of the new ones in, and now I'm having a problem. I'm trying to cold test the latest weld to see if there is a leak before I fire up the boiler this fall. According to the pressure gauge I'm at about 7psi (while it is filling). I'm not sure when the actual furnace is full so I've turned on the circulator to get some of the water from the storage tank into the boiler. When I turned on the circulator the new pressure relief valve blew (its set for 25psi, and that is the lowest it can be set for. I turned off the water and the pressure gauge reads 0, but while the circulator is on it blows the relief valve. What am I doing wrong?