Why Won't My Gas Water Heater Pilot Stay Lit?

The Short Answer: A standing pilot that lights while you hold the knob and goes out when you let go usually means the flame sensor (a thermocouple or thermopile) is not proving the flame to the gas valve. A pilot that stays lit for a while and then dies points more to combustion air, a clogged flame arrestor, a tripped thermal switch, or venting. Relight once per the label; then call a technician.

First, confirm you have a standing pilot

This page covers tanks with a small pilot flame that burns all the time and a gas valve knob marked OFF, PILOT and ON. Many power-vent models with a blower and power cord have no pilot; a hot-surface or spark igniter lights the burner, and the label says not to light it by hand. On those, a flame that will not stay on is an ignition or lockout problem; see whether an electronic-ignition heater can be lit by hand and the pilot and ignition problems hub.

Two kinds of standing-pilot controls

The likely cause depends on which gas valve the tank has.

A. O. Smith’s own service charts describe both types on its residential atmospheric tanks: the mechanical valve uses a thermocouple, and the electronic valve uses a thermopile and a status light that flashes steadily once the pilot is proven (mechanical valve chart (opens in a new tab), electronic valve chart (opens in a new tab)). State’s Select direct-vent sheet likewise lists a thermopile-powered electronic gas valve with an LED status indicator and a push-button piezo ignitor (State SRGSS04812 (opens in a new tab)). Flash meanings differ between controls, so read the chart printed on your valve rather than a chart from another brand.

Which brand family is your heater?

Store and private-label names come from a few manufacturers, which matters when looking up the right manual and parts.

• State, State Select, American, and Whirlpool tanks: A. O. Smith bought State Industries in 2001 and GSW, the parent of American Water Heater, in 2006 (A. O. Smith history (opens in a new tab); Contractor, 2006 (opens in a new tab)). Whirlpool-brand water heaters sold at Lowe’s were supplied by American Water Heater under a license announced in 2000 (Plumbing & Mechanical (opens in a new tab)). Confirm with the rating plate.
• GE tanks: In 1999 Rheem agreed to build GE-brand water heaters for The Home Depot (Supply House Times (opens in a new tab)). GE-branded heaters from other years may have a different maker; the rating plate names it. For Rheem-built tanks, see Rheem pilot light will not stay lit.

Common causes, by when the pilot goes out

Residential atmospheric gas tanks built to the flammable vapor ignition resistant (FVIR) requirements of ANSI Z21.10.1 have a sealed combustion chamber with a flame arrestor at the base, and A. O. Smith family tanks add a thermal switch near the combustion chamber. A. O. Smith’s charts treat a tripped thermal switch as a sign of an air-supply problem: the room must supply enough combustion air, and the flame arrestor and air filter may need cleaning.

What you can check safely

• No gas smell first. If you smell gas at any point, stop and leave.
• The gas supply. The handle on the shutoff valve in the gas line to the heater is open when it is parallel to the pipe. Check that other gas appliances work. On propane, check that the tank is not empty.
• The lighting label. Follow the lighting instructions printed on the heater exactly, once. They tell you how long to wait after turning the knob off, how to use the igniter button, and how long to hold the knob. The pilot can be hard to see in daylight; A. O. Smith suggests dimming the room lights to look through the viewport.
• The status light, if the valve has one. Count the flashes and compare them with the chart on the valve or in the manual.
• The space around the heater. Note lint, dust, sawdust, or stored chemicals near the base, a closet door that has been replaced with a solid one, and whether the pilot dies when a dryer, bath fan, or range hood runs. Keep gasoline, paint, and solvents out of the room.
• Write down the pattern. When it went out, how long it stayed lit, and the model and serial number from the rating plate.

If the pilot will not stay lit after one careful attempt, set the knob to OFF as the label directs and stop. Repeated relighting does not fix a failed sensor and can leave unburned gas in the combustion chamber.

What the technician will check

A technician confirms the gas supply and checks that the pilot flame is the right size and fully surrounds the sensor tip. They measure the thermocouple or thermopile output against the control maker’s specification to separate a weak sensor from a failed valve. If the thermal switch tripped, they find out why before resetting it, since it responds to poor combustion air or flame rollout. They inspect the flame arrestor and burner, run a draft test at the draft hood, and check the vent. Opening the sealed burner door and replacing a sensor, pilot assembly, or gas valve are gas and combustion work, and the door gasket must be resealed afterward. For more on the sensor itself, see thermocouple problems.

Repair or replace

A sensor, pilot assembly, thermal switch, or gas valve is a part replacement. Cleaning a flame arrestor or fixing combustion air is often the whole fix. A leaking tank means replacement, and A. O. Smith’s labels say a gas heater that has been under water must be replaced, not repaired.

Frequently Asked Questions

Q: Why does the pilot go out the moment I let go of the knob? A: While you hold the knob, you are holding the gas valve open by hand. When you release it, the valve stays open only if the thermocouple or thermopile is producing enough power from the pilot flame. If it goes out right away, the sensor, its connection, the thermal switch, or the valve is the likely cause. Holding the knob longer than the label says will not fix it.

Q: My pilot stays lit for a few hours, then goes out. Is that the thermocouple? A: Sometimes, but a delayed outage often points to combustion air or a clogged flame arrestor, which can trip the thermal switch on FVIR tanks that have one. A technician should find the cause before parts are replaced.

Q: Can I replace the thermocouple myself? A: On a sealed FVIR burner it means opening the combustion chamber and disconnecting a fitting at the gas valve, so it is technician work. Your part is the lighting label, the gas shutoff position, and observations.