Hi, this is my first post so please bear with me! I have an issue with my 2 speed circulation pump and I am looking for some help!

The wet end was leaking quite badly so I stripped it down and replaced both seals. I refitted the pump to my hot tub and it ran fine for 24 hours. Now when it try's to kick into the second speed it just humms? If I leave it on the 1st speed it circulates water fine and I can see the shaft spinning. When I clicked on the 2nd speed the shaft was still spinning although as I said there was a humming. After 30 secs of this humming I assume the motor is overheating as it cuts out.

So, I am a little bit lost! I removed the pump from the tub again and then ran it dry to see if the 2nd speed would kick in, and it does! So to clarify it looks like it the motor is fine until I put it under load as in let the water run through the motor.

Any ideas what this could be? I don't want to have to replace the pump as they are 300+!

Any advice would be greatly appreciated.