Just hooked up the spa and it seems to work ok, but the heater doesn't energize, or only at times. I am an HVAC tech, have knowledge and meters, but nothing on the schematic tells me when and why the heater energizes. Have seen it come on ( amp draw over 20 ) but only when the pump is on high speed. It was working fine last year, maintained setpoint, but moved it and now I'm not sure. Is there a time delay? Flow switch? Thanks for any info