I am having a problem with the heater on a 1984 Sundance Spa with the 605 Controller Board.

The "Flow" and "Heat" indicator lights come on with the thermostat, but the heater seems to only work intermittently, and the spa runs constantly in the "Heat" mode, but does not usually reach a temperature above 90 degrees.

This is a single 120V two speed Pump with a 240V heater.

When the "Heat" light is on, the "Heater In" connections on the 605 controller board show 240V, but the "Heater Out" connections usually show 0V. Sometimes the heater works, so somtimes I get 240V at the "Heater Out" connections on the 605 controller board.

The outbound side of the "Contactor" always shows 240V when the "Heat" light is on, and it sounds like it is working fine. The 240V power goes from the contactor through the 605 controller board, and seems to fail there.

I assume that this means that I need to replace the controller board, but I was also wondering if it might be possible to just replace one, or two of what seem to be solenoid relays on the controller board. The two solenoid relays that are closest to the heater connections are brown compared to the other relays, so I assume that one, or both of those relays have gone bad.

Does anyone know where I could buy replacement solenoid relays for a Sundance 605 controller board?

Also, if anyone thinks that I have incorrectly diagnosed this problem, I would be happy to know anything else that I should look at.

Thanks in advance for any advice.