Boiler shows F.10, may run at reduced output or lock out

Safety first: Turn off power and allow the boiler to cool before handling sensors.

• Locate supply sensor: The supply sensor is usually mounted on the outlet header or in a sensor well near the boiler's hot water outlet.
• Inspect wiring and connector: Check for loose, corroded, or damaged wires between the sensor and control board. Reseat the connector.
• Check sensor placement: Ensure the sensor is fully inserted into its well or securely clamped to the pipe with thermal paste if required.
• Reset and observe: Restore power and clear the fault. Compare the displayed supply temperature to an external thermometer on the outlet pipe. Large discrepancies or erratic readings indicate a bad sensor.
• Replace sensor: If faulty, replace with an OEM Lochinvar supply temperature sensor. Drain and isolate as needed if the sensor is immersed.

Professional help: If a new sensor does not resolve F.10, the control board may need further diagnosis.