SFS
Hayward
Stack Flue Sensor Fault
Heater shows SFS; unit will not fire or shuts down quickly.
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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 flue temperature sensor, Overheating in flue due to blockage, Loose sensor wiring, Incorrect venting configuration
How to Fix / Troubleshooting
Safety First: Turn off power and gas. Allow the heater and vent to cool before inspection.
- Inspect venting: Check the flue for obstructions or crushed sections that could cause high flue temperatures.
- Check sensor wiring: Locate the stack flue sensor on the exhaust outlet. Ensure its wires are intact and firmly connected to the control board.
- Test sensor: If you have a meter and the specifications, measure the sensor resistance at ambient temperature and compare to Hayward's chart. Replace if out of range.
- Replace sensor if needed: Install a Hayward OEM stack flue sensor and secure it properly to the flue.
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Repair Difficulty
Hard
4/5
Required Part
Stack Flue Sensor
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