Water Heater Pilot Light Keeps Going Out? Causes and Safe Fixes in Fort Collins

Why does my water heater pilot light keep going out?

The most common causes are a weak or misaligned thermocouple, a dirty pilot orifice, and a tripped thermal switch or flammable vapor sensor on an FVIR heater, often because lint is blocking the air intake. Drafts, venting problems, low gas or propane, and a failing gas control valve account for most of the rest.

What happens	Likely cause	Who fixes it
Goes out when you release the knob	Weak, loose or misplaced thermocouple; tripped thermal switch or ECO	Plumber
Small, yellow or flickering pilot	Dirty pilot orifice or tube	Plumber
Will not relight, or shows a lockout flash code (FVIR)	Thermal switch or flammable vapor sensor	Plumber, after finding the cause
Goes out every few days or after the burner runs	Short of combustion air, clogged intake screen or flame arrestor, vent problem	Clear the area; vent work needs a plumber
Goes out when a door opens, a fan runs or wind gusts	Drafts at the base or down the vent	Stop room drafts; vent work needs a plumber
Other gas appliances are out too, or propane ran low	Gas supply or pressure	Gas utility, propane supplier or plumber
Sizzling or water on the burner	Condensation after a cold fill, or a tank leak	Wait; call if water keeps coming
Everything else checks out	Faulty gas control valve	Plumber

Thermocouple and pilot problems

Bradford White’s service manual lists a poor connection at the gas valve, a thermocouple not fully seated in the pilot bracket, a flame that does not wrap the tip, and a weak thermocouple; Rheem specifies a flame covering the top 3/8 to 1/2 inch of the tip. Both brands also list a clogged pilot orifice or tube, which gives a small, yellow pilot.

A plumber tests the thermocouple with a millivolt meter before replacing anything. On an FVIR heater the repair means opening and resealing the sealed inner door, and Bradford White warns a breached seal can cause a fire.

FVIR thermal switch or flammable vapor sensor

Most 30- to 50-gallon gas water heaters built since mid-2003 are FVIR designs, according to Rheem: the sealed combustion chamber draws air through a flame arrestor at the base, so spilled gasoline vapors cannot ignite outside. A thermal switch shuts everything down if vapors burn inside, or if lint, dust or oil clog the arrestor and starve the flame (Bradford White).

Bradford White’s switch opens at roughly 240 to 290°F and has a red reset button, but resetting it without fixing the cause can simply trip it again; State’s handbook says the usual cause is poor combustion from a blocked vent or a dirty filter or arrestor. Some A.O. Smith models add a flammable vapor sensor that locks out with a flash code, and heaters with electronic ignition flag a weak flame sense rod or failed ignition the same way. A discolored flame arrestor means vapors burned inside: do not relight, because A.O. Smith and Bradford White say the heater must be replaced.

Air supply, drafts and venting

Rheem’s pilot-outage bulletin checks for downdrafts through the vent, fans, air rushing under a door, cramped closets and, on direct vent models, wind blowing into the outside terminal. The code’s standard method calls for 50 cubic feet of indoor air per 1,000 Btu/h of input, so a 40,000 Btu/h heater alone needs 2,000 cubic feet.

A blocked or undersized vent can also spill carbon monoxide, so soot, scorch marks or water at the draft hood mean shut the heater off and call. Our guide to water heater venting, from atmospheric to power vent explains each system.

Gas supply or a failed gas control valve

If other gas appliances are out too, suspect the gas supply; on propane, call your supplier before relighting if the tank ran low. If the thermocouple, pilot, air and gas pressure all check out, the gas control valve is the likely culprit. Bradford White calls it non-repairable, and a tripped single-use ECO means replacing the whole control.

What you can check, and when to call a plumber

You can safely check the gas valve, propane, drafts and clutter around the heater. Anything inside the combustion chamber, on the gas control valve or gas piping, or in the vent is a job for a licensed plumber.

You can check:

• That the gas shutoff valve is open and other gas appliances work
• The propane tank level
• Paint, gasoline, cleaners and laundry near the heater; move them away
• The air intake screen at the base: with the heater off and cooled for 10 minutes, vacuum off lint, as A.O. Smith advises at least once a year

Call a plumber when:

• The pilot goes out again after you relight it
• A thermal switch has tripped or the control shows a lockout code
• The flame arrestor is discolored, or you see soot or scorch marks
• Water is dripping on the burner

If a carbon monoxide alarm sounds, get everyone out and call 911. Every repair is done by licensed plumbers covered by liability insurance, with a written, itemized quote first; see water heater repair in Fort Collins and gas water heater repair. If the pilot stays lit but the water is cold, see our no hot water in the house troubleshooting guide.

When repeated pilot outages point to replacement

A pilot problem alone rarely justifies a new heater, because thermocouples, pilot assemblies and gas control valves are replaceable. Replacement makes sense after a flammable vapor incident, when a leaking tank drips water onto the burner, or when a new gas valve is poor value on an old heater.

For scale, Angi’s December 2025 national repair guide puts a thermocouple repair at about $150 or less and a gas control valve at about $350 on average, and the U.S. Department of Energy says most storage water heaters last 10 to 15 years. We give honest repair-or-replace advice; see water heater replacement in Fort Collins when it is time.