Pentair Pentair MasterTemp 400,000 BTU Gas Pool/Spa Heater AFS Error Fix: Air Flow Switch Fault

Error code AFS on the Pentair Pentair MasterTemp 400,000 BTU Gas Pool/Spa Heater means: Air Flow Switch Fault. The combustion air proving switch (air flow switch) has not closed or has opened during operation. This switch verifies that the combustion blower is moving adequate air through the combustion chamber and exhaust vent. Common causes include a failed combustion blower motor (the blower is not spinning or not reaching adequate speed), a blocked exhaust vent (leaves, bird nest, debris blocking the vent termination), a blocked combustion air intake, or a faulty air flow switch. Check the exhaust vent termination outside the building for obstructions. Verify the combustion blower motor is spinning when the heater attempts to fire. Replace the air flow switch if it is faulty.

The most successful fix is "Test and Replace Air Flow Switch or Combustion Blower Motor" (hard difficulty, ~60 minutes). Estimated DIY cost: $50-$100. 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 ("Test and Replace Air Flow Switch or Combustion Blower Motor") is rated hard difficulty and takes about 60 minutes. Tools needed: Phillips screwdriver, Multimeter, Nut driver set, Gloves.

DIY cost: $50-$100. Professional repair typically costs $250-$400. 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: AGS (Auto Gas Shutoff), bd (Board Error), BURNER DEBRIS (Burner Tray Obstruction), BYPASS VALVE (Bypass Valve Adjustment Needed), CF (Combustion Fan Fault), and 3 more.