My Grundfos pump hums and will not pump water. Turning it off at the power source for half a minute will resolve it, but this is happening more often. What might be the cause?

Does the motor turn it self off after a couple of minutes of no pumping?= ran out of water. If there is water up to the pump and still no water, check filter/s ( if there is any). Undo V band and check pump internals, impeller may be broken from shaft? When putting back together tap V band with block off wood or back of screw driver evenly as you do up the clamp to stop it distorting

Pump probably runs dry, try to fill up the pump with water a few times and see what it gives. If the pump heats up then the rotor is turning but no water moves, pressure is not building up. Pressure switch is maybe faulty. If you have the possibility to connect a pressure gauge after the dicharge you can see if the pressure is building up or not.

Question not 100% clear.

1) The pump is not working? Does the pump make a noise? if pump is not working full-time, it can cause delay in arrival.
If pump motor is suspect, and outlet has power, then check override switch located on timer. Set override to Timer, move some of the trippers outward, then manually rotate timer dial until pump turns ON.
http://waterheatertimer.org/images/IMG_9325-grundfos-timer-800.jpg
If no noise is detected, or noise stops and starts, or seems strained, or if pump is hot, then pump motor may have burned out.

2) If pump is working, and makes noise like a humming sound, and pump motor is not hot, but hot water is not circulating, then unplug pump so it will not overheat and burn up.
Disassemble the pump and cross-over piece. Clean piping with white vinegar or CLR. Do not soak in CLR or it will damage seals. Rinse parts thoroughly. Reassemble and see if problem is resolved.
If pump is vibrating, then suspects include sediment and/or air inside line, and this can be resolved by cleaning as described. Also install air vent to increase life of pump.

3) Other causes for hot water delay at faucet are crossover.
Crossover can be caused by bad single-handled faucet cartridge, and/or by clogged-or-failed check valve on cross-over piece on grundfos.
This type of problem lets cold water enter hot line, and causes delay in arrival of hot water. Clean-or-replace the grundfos cross-over piece, and replace bad faucet cartridge.
Open following link for testing instructions:
http://waterheatertimer.org/Crossover.html

Resources:
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/pdf/Troubleshoot-recirculation.pdf

Add a comment for more help.

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Question not 100% clear.

1) The pump is not working? Does the pump make a noise? if pump is not working full-time, it can cause delay in arrival.
If pump motor is suspect, and outlet has power, then check override switch located on timer. Set override to Timer, move some of the trippers outward, then manually rotate timer dial until pump turns ON.
http://waterheatertimer.org/images/IMG_9325-grundfos-timer-800.jpg
If no noise is detected, or noise stops and starts, or seems strained, or if pump is hot, then pump motor may have burned out.

2) If pump is working, and makes noise like a humming sound, and pump motor is not hot, but hot water is not circulating, then unplug pump so it will not overheat and burn up.
Disassemble the pump and cross-over piece. Clean piping with white vinegar or CLR. Do not soak in CLR or it will damage seals. Rinse parts thoroughly. Reassemble and see if problem is resolved.
If pump is vibrating, then suspects include sediment and/or air inside line, and this can be resolved by cleaning as described. Also install air vent to increase life of pump.

3) Other causes for hot water delay at faucet are crossover.
Crossover can be caused by bad single-handled faucet cartridge, and/or by clogged-or-failed check valve on cross-over piece on grundfos.
This type of problem lets cold water enter hot line, and causes delay in arrival of hot water. Clean-or-replace the grundfos cross-over piece, and replace bad faucet cartridge.
Open following link for testing instructions:
http://waterheatertimer.org/Crossover.html

Resources:
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/pdf/Troubleshoot-recirculation.pdf

Add a comment for more help.

Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

it's possible but not all that likely. The sump pump is pumping dirty water and the domestic water should be clean.

Sounds like it could be a blown capacitor in the motor. Disconnect from the power supply and remove the capacitor - it is usually situated undet the terminal box cover- examine it for leakage or distortion and replace it if necessary.

Humming noise is usually an indication of a bad motor.

Grundfos is a sealed unit and not a repairable item.
The timer dial should turn.
And pins located around dial control ON-OFF functions as timer dial rotates.


Does the receptacle have power?
If receptacle has power, and Grundfos is not working, then it is broken.
Grundfos manuals for UP series pumps do not show breakdown or parts list of any kind.
http://www.us.grundfos.com/web/download.nsf/Pages

Bigger question:
Why don't you have hot water?
Is water heater functioning?
Water heater is a separate appliance from Grundfos pump.
Grundfos pump circulates hot water from tank into the lines so there is no waiting for hot water ... but hot water heater should still make hot water.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Add a comment about water heater if that is also a problem.
You could have 2 problems, and water heater is main issue.

For do-it-yourself electric water heater repairs:
http://waterheatertimer.org/6DIY.html

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There are rebuild kits for this pump from Johntone Supply or Grainger Supply as well as others. A rebuild would be less then a complete new pump