On units equipped with a circulation pump the Moducontrol starts the circulation pump a few seconds after the cooling, heating or DHW caller is recognized. The pump continues to run as long as the Moducontrol receives a demand call.
Check the wiring connections at the MTA, Moducontrol (M1S-2, M1-2) and pump motor lead connections (wires 9 and 13). All pumps are 230 volts single phase. Check the pump windings for short, open, or grounded conditions. Remove the center cap on the pump. Using a screwdriver turn the pump shaft to test the tightness of the bearing. Pump should spin freely. Turn pump shaft several turns. Reinstall cap. Bleed air. Start and test. Check for closed valves in return or supply water.