Display shows “P1”; unit may not start or may run in a limited mode.

Safety first: Disconnect power before working inside the control compartment.

• Locate sensor: Find the primary water temperature sensor threaded or inserted into the water manifold.
• Check connection: Follow the sensor cable to the control board and ensure the plug is fully seated and free of corrosion.
• Compare temperatures: Use a pool thermometer to compare actual water temperature to the displayed value. Large discrepancies indicate sensor issues.
• Replace if needed: If the sensor is out of spec or P1 persists, replace the water temperature sensor with a Heat Siphon–approved part.