Boiler indicates 'Return Sensor Fault', 'Return Temp Open/Short', or return temperature is stuck at an extreme value.

Safety first: Power off and let the boiler cool before working on sensors.

• 1. Locate return sensor: Identify the sensor on the return piping or in a well on the return header.
• 2. Verify seating: Confirm the sensor is fully inserted and secured in the well or strapped tightly to the pipe with insulation over it.
• 3. Inspect wiring: Check for loose terminals at the control board and any visible cable damage.
• 4. Replace if necessary: Install a new Weil-McLain return sensor if the existing one tests open/short or the fault will not clear.