Spa pump cycles on and off when heater is on.

Hi folks, I've been troubleshooting a problem for a few days now. I'm still a little baffled and need some advice.

I have a Sunbelt spa with a gecko s-class control pack 240V. When I flip the breaker the tub boots, the pump comes on, but as soon as the heater is engaged the pump shuts off. I get three blinking lights up top. It continuously shuts itself on and off unless I lower the temperature to deactivate the heater. When I do so the three dots up top turn off and the pump will run normally.

I have read this site extensively and conducted the following tests without the filter in the tub:

I have tested the pressure sensor. It is switching on and off normally when the pumps are on/off.

If I hold the two pressure switch wires together the heater comes on but the pump turns off. (I can hear the water start to boil when the pump shuts off, scary)

I have removed the hi limit and jumped the hi limit both light up the red led on the board and nothing works.

The high limit sensor seems fine.

So my dilemma is, why does the pump shut off as soon as the heater relay activates. It's like an endless loop.

Pump comes on
pressure switch activates
heater relay engages
pump stops
pressure switch deactivates
heater deactivates
pump comes back on
pressure switch activates
heater relay engages.....
over and over again

For the last two years the tub as been doing this every once in a while and toward the end of last year it was getting worse. This year it just won't budge. I feel like it is mechanical for this reason. Yesterday I removed the pressure sensor and checked it for problems. It seems to be working fine. The ohm meter confirmed this.

The only thing I have to ad is last year the tub kept tripping the gf on the breaker. I tracked it back to the blower motor and once I unplugged the blower all worked fine. I'm not sure why that would make a difference in the matter above.

The spa's heater, control pack, and ozonator were replaced under warranty 5 years ago by sunbelt.

Any idea's or things to try. I hate to buy a pressure sensor when it seems to work correctly and jumping over the sensor still causes the pump to turn off.

Thanks,

Steven