Weil McLain F10

What does Weil McLain F10 mean?

F10 indicates the CH supply water temperature sensor 1 (the primary supply/discharge sensor) has gone outside its normal operating range due to a short circuit or open circuit condition. When the fault is active, all heat demands are disabled. If the sensor reading returns to a valid range, the fault clears automatically without a manual reset.

Symptoms

• Boiler displays F10 and stops heating.
• No central heating or domestic hot water output while fault is active.
• Fault clears temporarily then returns if sensor wiring is intermittently faulty.
• Boiler may default to using a secondary sensor if multiple sensors fail simultaneously.

Common causes

• Supply temperature sensor damaged or failed (open or short circuit).
• Sensor wiring shorted due to insulation damage or moisture ingress.
• Sensor wiring disconnected at the sensor body or control board terminal.
• Sensor connector corroded, producing intermittent resistance out of range.

Diagnostic steps

1. 01

   Identify the supply sensor 1 location

   Locate the CH supply temperature sensor on the boiler discharge pipe. Refer to the AquaBalance Series 2 boiler manual component diagram to confirm the sensor position.

2. 02

   Inspect sensor wiring for damage

   Visually inspect the wiring from the sensor to the control board for pinching, burn marks, or bare wires. Repair any insulation damage found.

3. 03

   Check wiring connections

   Unplug the sensor connector and inspect for corrosion or bent pins. Re-seat the connector firmly and reset the boiler. If the fault clears, monitor for recurrence.

4. 04

   Measure sensor resistance

   With power off, disconnect the sensor and measure its resistance with a multimeter. Compare the reading against the temperature-resistance table in the boiler manual. An open circuit (infinite resistance) or short (near zero ohms) confirms a failed sensor.

5. 05

   Replace the sensor if defective

   Install a genuine Weil-McLain replacement supply sensor. Restore power, reset the boiler, and confirm F10 no longer appears during a heating cycle.

When to call a professional

Call a licensed technician if sensor replacement does not clear F10 or if the fault reappears quickly after a new sensor is installed. Persistent F10 after component replacement points to a control board input circuit failure; board-level diagnosis and replacement must be performed by a qualified technician.