Grundfos UP15 Circulator pump quits when it gets hot

BP3

I have a Grundfos UP15-18SU that circulates DHW thru a solar heat exchanger that I have now determined only runs when it is cool. I have removed it and tested it on the bench, and it runs (it was cool). Impeller is free, all air is bled, system has been working as-is for years.

I reinstalled it and verified it was pumping fluid when cold. After running for a while, it gets hot and stops. I checked and there is power when it is not working. I am convinced it is the pump. I could replace it, but a cheaper option would be to replace just the cartridge. Is there an effective way to determine if the cartridge is bad vs the stator? (in which case I would need to replace the pump).

hot_rod

15-18, that must be pretty old? Date code is stamped on end plate, week/year 4 digits.
Power stays on pump when it quits spinning? Making sure it is the motor not a control.

BP3

Yes, I checked and verified with a meter that power is there when the motor stops. I checked all connections. It is also wired in parallel with the glycol circulator and it is running when it should be.

BP3

Date code is 8517...yes it is old but. I removed the end cap yesterday when hot and turned on manually and the shaft was not turning, but was free and not bound up. This am (cool) I did the same and the motor runs when turned on.

I know the newer ones have internal thermal protection but can't determine if this one does. Does anyone know any details on the thermal protection on these motors? (just looking for a temp solution as the glycol is baking without the heat exchanger drawing heat)

HVACNUT

A temp solution would be to replace the circulator, permanently. 

BP3

I have one on order, just don't want to bake my fairly fresh PG.

EBEBRATT-Ed

The motor should have thermal protection which could be opening.

Check the motor amps and voltage to see that they are within spec.

Try throttling the valve in the discharge pipe (do not close the suction valve) with an amprobe on the pump wire and see if closing the valve a little drops the amps and takes some load off the pump which may allow it to run

HomerJSmith

I don't know if this helps, but...Years ago, there was a lightning strike near a home with Grundfos pumps in a hydrolic sys. The lightning strike knocked out all of the pumps. These were expensive pumps. I wanted to know why they failed. Most service techs would have replace them and went home smiling. Not me. So I took one apart and discovered a circuit board between the pump windings and the cap and power in. The lightning strike had fried (melted) the circuit board foil connections. So, I made my own circuit boards, I can do that, and soldered them in, walla, worked perfectly. Now to my point, perhaps the solder joint on your circuit board if you have one in that pump has a loose connection. Look at them under magnification and if you see a cold or cracked solder joint touch it up. The circuit board is under the plastic wiring box.

Your symptoms fit that scenario perfectly. Runs when cold, stops
when hot.

It could be a thermal protection as Ed suggest or a loose connection.

A locked rotor will increase the temp, as I recall. A solder ball in the impeller can lock a rotor.

BP3

Thanks, HomerJSmith, I will take a look at that.