MiniMax 400 not heating

[timd]

I have a MiniMax 400 pool heater that is not heating. Only the power light is on the front of the control board, but sometimes the thermostat light will be on also. I just replaced the circuit board about 2 years ago, due to the same similar issue, could this be the same problem again? When I look at the back of the board with the pool running in spa mode, none of the 3 lights on the back of the board (PV, TFUSE, HITEMP) are lit up, but not sure it they should be or not.
Any ideas would be appreciated.

 

[kadavis]

Does the pressure lite come on. If not start there. If your familiar with using a voltmeter check the different wires connected at the top of board. Should get 24V checking each wire.https://www.manualslib.com/manual/918823/Pentair-Minimax-Plus.html?page=22#manual