F.11
Lochinvar
Return Temperature Sensor Fault
Boiler intermittently shows F.11, especially during high demand
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed return sensor, loose harness, sensor shorted by moisture, incorrect sensor type installed
How to Fix / Troubleshooting
Safety first: Disconnect power before working on sensors or wiring.
- Locate return sensor: Typically installed on the return header or in a sensor well on the return piping.
- Inspect for moisture: Look for signs of water intrusion around the sensor or wiring. Dry any moisture and correct leaks from nearby fittings.
- Check wiring: Ensure the sensor harness is intact and not pinched under panels or clamps. Reseat the connector at the control board.
- Reset and monitor: Restore power and clear the fault. Monitor the displayed return temperature for stability.
- Replace if needed: Install a new Lochinvar return sensor if readings remain erratic or F.11 recurs.
Professional help: Persistent sensor faults after replacement may indicate a control board issue.
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Repair Difficulty
Medium
3/5
Required Part
Return Water Temperature Sensor
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