Pentair Pentair MasterTemp 400,000 BTU Gas Pool/Spa Heater SFS Error Fix: Stack Flue Sensor Fault

Error code SFS on the Pentair Pentair MasterTemp 400,000 BTU Gas Pool/Spa Heater means: Stack Flue Sensor Fault. The stack flue sensor has an open circuit or short circuit. The sensor itself has failed, as opposed to E05/E06 where the sensor is working but reporting high temperature. The heater cannot monitor exhaust temperature without a functioning sensor and will not operate. Replace the stack flue temperature sensor. Check the sensor cable for damage and the connector for corrosion.

The most successful fix is "Replace Stack Flue Temperature Sensor and Inspect Wiring" (medium difficulty, ~45 minutes). Estimated DIY cost: $15-$30. HomeMD has 2 community-ranked fixes for this error.

This error is rated critical severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Replace Stack Flue Temperature Sensor and Inspect Wiring") is rated medium difficulty and takes about 45 minutes. Tools needed: Multimeter, T20 Torx screwdriver, Needle-nose pliers.

DIY cost: $15-$30. Professional repair typically costs $120-$200. Many homeowners save money by trying the top-ranked community fix first.

The Pentair Pentair MasterTemp 400,000 BTU Gas Pool/Spa Heater has 8 other known error codes, including: AFS (Air Flow Switch Fault), AGS (Auto Gas Shutoff), bd (Board Error), BURNER DEBRIS (Burner Tray Obstruction), BYPASS VALVE (Bypass Valve Adjustment Needed), and 3 more.