I have a 1995 cal spa model PS-5-B the GFI tripped when the heat came on and the low speed motor

I finally got the GFI to stay on when I turn up the thermostat to turn heat on the indicator light goes on but not the low speed side of pump.

The high speed side of pump works fine on switch until I turn up thermostat then it trips the GFI

Unplugged the flow switch plug last night and heat came on and low speed side of pump its been running for almost 20 hours now and the water is warm but not hot should've only taken 12 hours to fully heat water could this be a bad pressure switch or is the flow switch bad ?

If you unplugged the flow switch, the heater is not actually coming on... any heat you might be gaining is coming from excess heat from the pump and kinetic energy.

The #1 cause of a tripping GFCI is a bad heating element.

If you can rephrase your description... with some punctuation, and more individualized thoughts, I may be able to figure out more.

Thank you I just turned it off.

Is there a way to test the heating element? I have a multi-meter.

Also if it is bad, how do I find the part number I can't seem to find the specs

1995 cal spa model# PS-5-B Mechanical not electronic