IQ2020 -- Siberian L heater issue

[capntank]

Hey everyone! I recently moved my 2002 Tiger River Siberian L to a new house and I'm having an issue that I can not resolve.
When I power up the tub it seems to be getting air into the heater and tripping the relay. If I turn the power on at the breaker and then immediately turn on one of the blowers it will run like normal, until the end of the cycle, where it will eventually turn off the blowers and the problem will occur again.

What I've done so far:
- I replaced a good amount of the water lines in around the motors/heater.
- Took the heater out, cleaned it, didn't notice any cracks in the housing. All of the seals look ok as well.
- Took the small circulating motor off, plugged it directly into 110, seems to be working fine.

What I know:
- The heater element is working correctly.
- The two blowers still work great, and when operating I do not see air getting into the system.
- As soon as said blowers are turned off I can hear the heater turn on, and visibly see an air bubble forming in the line coming out of the heater. If I quickly turn on the blower it dissipates the bubble and the relay will not turn off the tub.

Parts in it:
Watkins SilentFlo 5000
No Fault Heater - (Titanium) 6kW @ 240V - 1.5kW @ 120V -or- 4kW @ 240V - 1kW @ 120V

Thanks in advance for you help, I really appreciate it!

-Mike

[capntank]

fixed it! I decided to start replacing parts in line and I began with the circulating motor. It was still working but something was strange about it. Put a new one in, and the problem is gone.

[Tman122]

fixed it! I decided to start replacing parts in line and I began with the circulating motor. It was still working but something was strange about it. Put a new one in, and the problem is gone.

I was going to say circ pump, but waited to see if any of the other professional service dudes replied. Good work.