SCP-120 will not actuate the relay panel when it is calling for heat, or it will continuously call for heat even when it is manually cycled on & off.
Verify if conduit is being run into the top of the SCP-120 box. If conduit is running into the top of the controller box, condensation may have formed inside the conduit and dripped down onto the circuit board inside the SCP-120. If this is the case, the unit will need to be replaced.
If there is no conduit entering the box from above, there may be a problem with the relay inside the box. This relay is visible when the cover is removed. If the 24v trigger voltage is always on, the board has been dameged inside the unit. If the 24V switches on and off as the manual switch is thrown, the relay is stuck on or off. The relay can be bought from the 2 following websites: