There has been a humming noise coming from the hot water heater, and it sounds like it's coming from the Grundfos UP 15-18 B5 pump. The humming is constant 24 hours a day and from what I can tell it is NOT affecting the performance of the water being heated and sent into the house.
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Did you try disconnecting power to the pump to confirm that it is the cause? I would not want to recommend a repair until the root cause is ascertained. – Jimmy Fix-it Apr 05 '16 at 03:32
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Thanks for the heads up Jimmy. I unplugged the pump and the humming stopped. Do you know if there are settings are a reset on the pump to keep it from humming or is that normal for the pump to hum? – user52326 Apr 05 '16 at 04:56
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They usually do not run continuously, most hot water recirc pumps have a thermostat control switch (a heat sensing button that lays on the pipe with wires to the pump) and/or a timer control. A low hum would be normal... could it be vibration? If you turn it back on and grab the pipe (with gloves) does the hum change? – Jimmy Fix-it Apr 05 '16 at 05:35
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After nobody has been using hot water for a while (like early morning), with the pump on, go to your most distant hot water tap and see if you get hot water right away, to see if it's pumping. Is this hum something new? – Jimmy Fix-it Apr 05 '16 at 05:40
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You can check to see if the impeller is frozen/locked up: switch off the power supply and close isolation valves on each side of the pump. Remove the indicator plug in the middle of the nameplate. Insert a small flat-blade screwdriver into the end of the shaft and gently turn until the shaft moves freely. Replace and tighten the plug. Open the isolating valves and wait 2 to 3 minutes for the system pressure to equalize before starting the pump. – Jimmy Fix-it Apr 05 '16 at 05:59
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No reset, they have a thermal shutdown to protect the motor (if the impeller gets stuck they will heat up). They automatically reset when they cool off. – Jimmy Fix-it Apr 06 '16 at 03:01