F20
Thermeau
Safety Circuit Open (Limit Chain / Flow / Pressure)
Heater shows F20; may be associated with internal safety chain faults.
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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
Open high limit, open flow switch, open air pressure switch, Loose connection in Thermeau safety circuit wiring harness
How to Fix / Troubleshooting
Safety first: Turn off power and gas. Never bypass safety switches for operation.
- Check wiring harness: Locate the safety circuit harness that daisy-chains the flow switch, high limits, and pressure switches. Inspect for loose or disconnected terminals.
- Test individual switches: With a multimeter and heater off, check continuity across each safety device. Any that remain open under normal conditions may be faulty.
- Inspect for overheating or low flow: If a high limit is open, investigate flow and temperature issues before resetting or replacing.
- Secure connections: Re-seat all spade connectors and ensure they are tight on the switch terminals.
- Replace failed safety devices: Install genuine Thermeau replacements for any defective switches.
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Repair Difficulty
Medium
3/5
Required Part
Thermeau Safety Switch Harness
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