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That's normally where I go first too. Replaced it. No difference. Today I circulated till it was up to temp and the pump shut off, there's a few seconds and then I hear the heating element boiling the water in the pipe till it kicks out the overheat switch. I waited a few minutes and pushed the "on" button again. The stand-by blinking light went off and it didn't circulate because it was already up to temp but I heard the water in the pipe start to boil again so I unplugged the flow sensor wires and it continued to boil till it kick out again. The flow switch has no effect on the over heat Robertissue.