Replaced the wet end (FMCP part # 91040820) on a Magnatek 1.5 HP pump following the directions shown on Spasupport.com. The pump works fine on low speed, and will run all day. When switched to high speed, it will run for a few minutes and then shuts down for several seconds. Then it will run for about 20 seconds and then shut down for about 15 seconds and continues that cycle until it times out. The motor feels warm to touch and it appears that the thermal switch is tripping. Tried disconnecting the suction end of the pump and let the water flow back and saw no indication of debris. Haven't tried to reassemble the wet end yet. Any suggestions?

This may sound stupid, but are you positive the motor is actually shutting off? When a thermal overload trips in a motor, they won't reset in a few seconds. It will take minutes to reset. However, if the pump is drawing in air from somewhere, it will loose prime and "freewheel" by not pumping any water until it gets a prime again. When this happens, it will surge. This will go on for a few seconds of surge, then a few seconds of nothing, then the cycle starts all over again.

Charger 1,

Thanks for the response. It may be sucking air from somewhere. Why would it work OK in low speed though, and not in high? Any suggestions on how to check for air surge?

Porter Ellis

On low, you aren't drawing a lot of water from the tub, but in high, you are pulling a lot of water. If there is a small air leak, on low, it could draw air in but it wouldn't be enough to loose the prime. That same small air leak could become a major source of air into the system when drawn at high speed.

When you get a chance, turn the tub on high, and when it quits flowing, look at the pump shaft and see if it is still turning. If it is, then you have an air induction problem. If not, then you will have to search elsewhere for the reason why the motor is cutting out. If it does stop, check to see if it is humming. If it is, then some motor work is likely in order.

Charger_1

Thanks for the info. I'll check it out.

Porter Ellis

if you've just replaced the motor, there's a good chance its either faulty or you've ordered an undersized motor for the hp rating of your impeller - i'd suggest reassessing this area as its definetely the most likely problem - on low speed you won't see a problem, but on high the motor won't be able to handle the load of a larger impeller, overheat and trip the thermal protection

in addition to the above - if the motor sounds really grindy/noisy and its actually less than 20 secs, you could have a stuck low speed circuit board relay - this causes both low and high to receive power simultaneously when high is selected making the pump motor very unhappy

call a service tech

Alacy,

Thanks for the input. The motor is the existing motor - just replaced the wet end. Could be a relay, may have tocall a tech.

Charger_1

The motor is actually shutting down and cycling on and off on high. Thanks