An AO Smith flammable vapor sensor code usually means the heater detected fuel vapors and locked out on purpose. Most clears take 10 to 20 minutes and are a DIY job if the area is safe, but recurring lockouts, gas odors, or sensor replacement call for a licensed pro.
Start by treating the code as a safety shutdown, not a nuisance. If you smell gasoline, paint thinner, solvent, or raw gas, stop and leave the area before touching the heater.
If the room is clear and the unit still shows the code, the usual job is to ventilate, check nearby chemicals, then follow your model’s reset steps. A repeat code points to the sensor, wiring, or venting setup, not a bad day for the display.
The essentials
Open the area, remove fuel cans and solvent products, then try a reset only after the air is clear.
Do not keep resetting a heater that trips again right away; repeated lockouts mean the problem is still there.
A flammable vapor sensor is a safety part, so a bad sensor or contaminated area can both cause the code.
If you smell gas or suspect a leak, stop and call the gas company or a licensed technician.
Replacing the sensor is a parts-and-safety job, not a brute-force fix.
How to Clear a Flammable Vapor Sensor Code on AO Smith
If your AO Smith hot water tank shows a flammable vapor sensor lockout, the first step is to remove any source of fuel vapors like gasoline, paint thinner, or aerosol sprays from the area. Yes, you can reset the flammable vapor sensor (FVS) on an AO Smith water heater, but only after the air is clear and safe.
Ensure the area around your water heater is clear.
Safety First
If you smell gas or strong fuel vapors near your water heater, do not try to reset the sensor or turn the heater back on. Leave the area immediately and call for professional help.
To clear the lockout safely, follow these key steps: turn off the heater if your manual says to, ventilate the room well, remove any stored chemicals or solvents, wait until the vapor smell dissipates, then perform the reset using the procedure labeled on your unit or in the manual. The sensor reset only clears the lockout if the surrounding air is clean. It won’t fix ongoing problems like fuel leaks, poor ventilation, or a faulty sensor.
1
Turn Off the Heater
Switch off the water heater power or gas supply as instructed by your model’s manual to prevent accidental ignition.
2
Ventilate the Room
Open windows and doors or use fans to clear out any lingering fuel vapors from the area around the heater.
3
Remove Fuel Sources
Take out gasoline cans, solvent containers, aerosol sprays, paint thinner, or anything with a strong fuel smell near the heater.
4
Wait for the Air to Clear
Give the space at least 10 to 20 minutes to ensure no flammable vapors remain before attempting a reset.
5
Reset the Sensor
Follow your AO Smith water heater’s reset procedure found on the unit label or in the owner’s manual. This typically involves pressing a reset button or cycling power.
Replace the Sensor If Needed
SP20172 Flammable Vapor FV Sensor Kit | AP13447-3
If the lockout persists after clearing vapors, a sensor replacement may be necessary using a kit like product 1, which fits AO Smith models and restores proper vapor detection.
Owner’s manual or your water heater’s model number to find the reset procedure
Replacement flammable vapor sensor kit if the sensor is faulty
In short
Remove all fuel vapors first, then ventilate and wait. Only reset the sensor after the air is safe; otherwise, the lockout won’t clear and you risk fire. Persistent codes or gas odors mean call a pro.
What You’ll Need
Use only the tools and parts that match your model and the job in front of you.
Sensor replacement kit
WAO ZONE Flammable Vapor Sensor Kit AP13447-3
This kit includes the exact flammable vapor sensor that fits AO Smith models and related brands, plus a cap plug and wire tie for a complete replacement setup. It quickly restores your heater’s safety function by detecting vapors and cutting off gas supply to prevent hazards.
The AO Smith flammable vapor sensor is a safety device that detects hydrocarbon vapors near your water heater and tells the control board to lock out the burner before ignition. This prevents fires or explosions caused by nearby gasoline, paint thinner, or solvent fumes.
Common trigger sources include gasoline spills, paint thinner containers, solvent fumes, aerosol sprays, and any fresh fuel spills near the heater. These vapors are flammable and the sensor reacts quickly to cut the gas supply.
Trigger Source
Typical Vapor Type
Risk Level Near Heater
Gasoline
Hydrocarbon
High
Paint Thinner
Solvent
High
Solvent Fumes
Hydrocarbon
High
Aerosol Products
Propellant Hydrocarbons
High
Spills Near Heater
Mixed Hydrocarbon
High
Normal Humidity
Water Vapor
Low
Common causes of flammable vapor sensor activation versus harmless moisture.
Myth
Humidity triggers the flammable vapor sensor frequently and is the main cause of lockouts.
Fact
Humidity may cause occasional nuisance triggers in highly humid rooms, but repeated lockouts almost always mean real hydrocarbon vapors or a sensor problem. Don’t ignore recurring codes expecting humidity to clear it.
You might wonder if low LP gas pressure can cause a flammable vapor sensor lockout on an AO Smith LP water heater. Low gas pressure can cause burner ignition or flame issues, but it does not directly trigger the vapor sensor circuit. That sensor watches for vapors around the heater, not burner performance. If you see a vapor sensor fault detected, check vapors or the sensor first.
The exact flash code or display text for a flammable vapor sensor lockout varies by AO Smith model. For instance, the AO Smith 50 gallon hot water tank may show Flash Code 7 for flame vapor sensor trouble. Your manual and model number are key to interpreting the message accurately.
In plumbing, a vapor sensor is a device installed near the gas burner or combustion air intake that detects dangerous vapors before ignition. It enhances safety by preventing the heater from lighting if flammable vapors are present.
Fix The Mistakes That Damage The Heater
AO Smith flammable vapor sensor lockout often comes from avoidable mistakes that damage your heater or cause repeated faults. Common errors include storing gasoline or solvent cans in the heater closet, spraying aerosol cleaners nearby, covering combustion air openings, and resetting the heater repeatedly without removing vapor sources.
Avoid storing flammable items near your heater.
Damage Risks From Mishandling
Forcing an incompatible sensor part, bending or pinching sensor wires, or leaving spilled fuel near the heater can damage the control board or create unsafe conditions. Repairs become costlier and the heater may not light reliably.
If the flammable vapor sensor fault persists after clearing the area, the sensor itself might be contaminated or its wiring damaged. A heater located where fumes naturally collect or enter can keep triggering the code despite your best efforts.
Replacing the flammable vapor sensor assembly can fix recurring lockouts if the heater is otherwise sound and your model uses a user-replaceable sensor. Make sure you use the sensor only as a replacement part, not as a general fix for unrelated issues.
Use this replacement kit for sensor faul
SP20172 Flammable Vapor FV Sensor Kit | AP13447-3
The SP20172 Flammable Vapor FV Sensor Kit includes the sensor and all parts needed to replace your AO Smith vapor sensor and clear the lockout safely.
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When You Need A Permit Or A Licensed Pro
You can usually reset an AO Smith flammable vapor sensor code yourself if the area is safe and free of fuel vapors. If your hot water tank shows a flammable vapor sensor lockout, start by clearing the area of any gasoline, paint thinner, or aerosol sprays and then perform a proper reset.
The flammable vapor sensor in plumbing is a safety device that detects hydrocarbon vapors near your heater and prevents ignition to avoid fire or explosion. If you smell gas, see damage to vents, or suspect air supply changes are needed, do not attempt repairs yourself.
When to call a pro
Any work that involves opening the gas line, repairing the venting system, adjusting the burner compartment, or changing sealed combustion parts should be done by a licensed plumber or gas fitter. Local codes often require permits for these tasks, and guessing risks safety and compliance.
If the lockout happens repeatedly despite correct resets, this indicates the safety system is not satisfied. A service call is necessary to diagnose the underlying issue rather than ignoring or repeatedly resetting the code.
Local regulations matter
Some states and cities regulate gas appliance work more strictly than a homeowner repair allowance. Check your local code before doing anything beyond a reset. When in doubt, hire a licensed professional.
What To Do Next
If you detect a fuel smell in the room, stop immediately and leave. Do not try to reset the AO Smith flammable vapor sensor. Safety comes first.
When the area is clear and the sensor fault stays after one proper reset, inspect for stored chemicals or poor ventilation. These can cause false triggers and should be removed or improved before replacing parts.
If the lockout returns after addressing environmental factors, replace the sensor only if your model allows and you are comfortable with gas appliance work. Otherwise, scheduling professional service is the safest choice.
Should the heater continue to lock out, have your model number and exact error code ready for the service technician to speed up diagnosis and repair.
Next steps checklist
Clear the area of fuel vapors and chemicals
Reset the flammable vapor sensor once following manufacturer instructions
Decide between sensor replacement or calling a licensed professional
In short
An AO Smith flammable vapor sensor lockout warns of danger. Reset once if safe, then check your environment. Replace parts or call a pro if the problem persists.
More Questions, Answered
Can you reset an FV S on an AO Smith water heater?
Yes, you can reset a flammable vapor sensor (FVS) lockout on an AO Smith water heater by following the manufacturer’s reset procedure, usually involving turning off the power or gas supply and waiting 10 to 20 minutes for the sensor to clear. Make sure the area is free of fuel vapors before attempting a reset to avoid repeated lockouts or safety hazards.
What does a flammable vapor sensor fault detected code mean?
This code means the heater’s sensor detected hydrocarbon vapors near the unit, which triggers an automatic lockout to prevent ignition and a possible fire or explosion. It’s a safety response indicating the presence of flammable vapors in the heater’s vicinity.
What causes FVS lockout on an AO Smith LP water heater?
FVS lockouts happen when flammable vapors like gasoline, paint thinner, or aerosol sprays are stored or spilled near the water heater. Poor ventilation or leaks in fuel containers can also cause vapor buildup that the sensor detects, forcing the heater to shut down.
Will low LP gas pressure cause an FVS lockout on AO Smith?
Low LP gas pressure itself does not cause an FVS lockout, as the sensor detects vapors, not gas pressure. However, improper gas pressure can cause other faults or operational issues that might be mistaken for sensor problems.
What is a vapor sensor in plumbing?
A vapor sensor in plumbing, like the flammable vapor sensor on AO Smith heaters, detects the presence of combustible hydrocarbon vapors in the air near the appliance. It serves as a safety device to prevent ignition when fuel vapors are present, protecting against fire hazards.
Where is the reset button on an AO Smith water heater?
The reset button location varies by model but is often found behind the access panel on gas models or near the thermostat on electric models. Consult your heater’s manual or Where Is the Reset Button on an AO Smith Water Heater? for exact instructions.
Should I replace the flammable vapor sensor if the code keeps returning?
Recurring FVS codes usually indicate a persistent vapor source or a faulty sensor. If you have eliminated all vapor sources and the code returns, sensor replacement is likely needed. Have a licensed technician confirm the diagnosis and perform the replacement to ensure safety.
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Water Heater Owner's ToolkitFix the common faults yourself, keep it running for years, and know when a repair is money wasted.No-hot-water flowcharts, gas and electricFlush, anode, relief valve and descaling stepsRepair-or-replace calculator (Excel)