AO Smith 6 Flashes: Flammable Vapor Sensor Lockout
The status light on your AO Smith gas water heater is blinking six times in a row, pausing, then repeating — and the burner won't fire. That pattern points to the FVIR system's flammable-vapor sensor doing exactly what it was designed to do.
Applies to: AO Smith gas storage tank water heaters with electronic ignition/FVIR gas control (ProLine, Signature, and similar residential tank models)
What it means
Flammable Vapor (FV) Sensor Lockout — the unit's flammable-vapor sensor detected vapors it treats as a fire hazard and shut the gas valve down as a safety measure. AO Smith's FVIR (Flammable Vapor Ignition Resistant) design cuts gas flow the moment this sensor picks up vapors it's tuned to recognize, rather than waiting for something to spark near the burner. The six-flash pattern is the water heater confirming that's what tripped, not a random control-board glitch.
Most common causes
- Gasoline, paint, solvents, or other flammable liquids/vapors stored or used near the water heater
- Dust or lint buildup on the sensor
- Sensor malfunction
What you can safely check yourself
- Remove any flammable liquids, aerosols, or solvents from near the water heater and ventilate the area
- Follow the reset procedure printed on the gas control valve label once the area is clear
When to call a professional
The lockout keeps recurring with no flammable materials anywhere near the unit — the sensor or gas valve likely needs replacement. Never disable or bypass this safety feature.
Gas control valves and the flammable-vapor sensor system should only be inspected or replaced by a licensed plumber or HVAC technician — never bypassed or taped over.
What the fix costs
Most six-flash lockouts cost nothing to resolve — clearing stored solvents and pressing the reset button on the valve label is free. If the sensor itself has failed and a technician determines it needs replacing, that's a gas-valve-adjacent repair that typically runs $150–$450 installed, in line with Angi's and HomeGuide's water heater repair guides; a diagnostic visit alone for a recurring lockout tends to land at $150–$300. These are national ballpark ranges, not a quote for your specific unit.
Related codes
- AO Smith 4 Flashes — High-Temperature Limit (ECO) Trip
- AO Smith 7 Flashes — Gas Control Valve Failure
- AO Smith 2 Flashes — Low Thermopile Voltage
All AO Smith codes
Every AO Smith water heater fault code — the full list on one page. More broadly, this falls under water heater ignition failure — worth a look if you're troubleshooting beyond just this one code.
Sources
- AO Smith gas water heater status light / blinking fault code chart (manufacturer documentation)