I have a 1992 Sundance Montego LX spa with 230 volt service and using Sentry 600 series electronics (MT3400-MT62706) . I recently replaced the main pump with a new one and when I turned the tub on, I couldn't get the heat to turn on (no heat and no heat lamp lit on spa control panel). I checked the flo switch (works OK and the flow LED works on the control panel). There is no voltage (240V) at the heater terminals. I also noticed that the clock/timer doesn't work and doesn't cycle through low speed when in Economy mode when manually rotated. Is there a connection? I had read that a contactor could be the problem, but I cannot find one on this model.

That would leave the possible solution to be replacement of the circuit board. However, I see that there is a 600 Series and a 624 Series board. If this is the solution, which one would I need since it appears that the 624 is for 240 volts? Is there anything else that would cause the loss of heat?

Thanks.

The 1992 Sundance Montego uses the 400 series suncoast controls with a 600 series label on it.
Basically if the low speed pump works <--- Very important, and the system is not heating then you have no choice but to replace the circuit board (temp sensors wouldn't be a bad idea either)...If the low speed pump does not run then you need to see if it is getting voltage, usually if the high speed pump works then the low speed will also and therefore your problem would be the circuit board still, however if the pump does get voltage then you will need to replace the pump motor.

877-936-2223
part #6600-032 Circuit board