Water Heater Pilot Light: Lighting It and Keeping It Lit

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the sources at the end

Water Heater Pilot Light: Lighting It and Keeping It Lit

Short answer

Turn the gas control to off and wait ten minutes before anything else. Then hold the knob on pilot while you click the igniter, and keep holding it for a full minute after the flame catches. A pilot that lights and then dies the moment you let go is almost always the thermocouple, a twelve dollar part.

A water heater pilot light is the small flame that burns all the time so the heater has something to light its main burner from. When that flame goes out, the gas valve shuts everything down and the water goes cold. That is the whole story.

Lighting it again takes five minutes. The part that matters is what happens next: a pilot that lights and then dies the second you let go of the knob is telling you something specific, and it points at one cheap part.

Before you start

Is your heater gas? If there is no gas pipe and no burner under the tank, you have an electric heater and there is no pilot on it at all. The part that fails there is the thermostat or the element: how to test a water heater thermostat.

What to carry down: a torch, a multimeter if you have one, and a mirror is handy for seeing the burner. Most heaters made in the last twenty years light themselves with a built in igniter, so you do not need a match or a long lighter, and on a sealed chamber you must not use one.

Ten minutes for the lighting. Half an hour if a thermocouple turns out to be the problem.

If you smell gas, stop Leave the house, leave the door open and call the gas company or the fire brigade from outside. Do not touch a light switch, a phone or the heater. A pilot is a small job, gas in a room is not.

Light it, in the right order

The knob has three positions, and the flame has to wrap the tip of the rod sitting in it.

1. Turn the gas control knob to OFF. The dial on the front of the heater, the one with the temperature marks. Press it down slightly if it will not turn.

2. Wait ten minutes. This is not optional and it is not being careful for the sake of it. Rheem’s lighting label warns that some gas is heavier than air and settles on the floor, which is exactly where the igniter sparks. A.O. Smith says to wait at least ten minutes to let it clear.

3. Turn the knob to PILOT and hold it down. Holding the knob is what lets gas reach the pilot at all.

4. Click the igniter while you hold. The button on the front, usually red or black. Click it once a second. You should see the flame through the little window near the bottom of the heater, and on some heaters hear it catch.

5. Keep holding for a full minute. This is where most people fail. The rod sitting in that flame has to get properly hot before it can hold the gas valve open on its own. Thirty seconds is not always enough. Sixty is.

6. Let go, then turn the knob to ON and set the temperature to 120. The main burner should light within a minute or two if the water is cold.

It lights, then dies when I let go

This is the common one, and it has four causes. Work down them in this order, cheapest first.

Check 1Twenty minutes

The thermocouple, the rod sitting in the flame

That rod makes a tiny electric current when it is hot, and that current is the only thing holding the gas valve open. When it weakens with age, the valve closes the moment you stop holding the knob.

With a meter on millivolts, unscrew the rod’s nut from the gas valve, hold the pilot lit, and read across the rod’s end and its sleeve. Bradford White’s service manual calls 20 to 30 millivolts good output on this test. Well under that and it is finished. A thermopile, the fatter two wire type on heaters with a digital display, should read 350 to 850 millivolts, Bradford White and Resideo say.

No meter? Change it anyway. It is the cheapest part on the heater and it is the usual answer.

Check 2

The flame itself

Look at the flame through the window. It should be blue, steady, and big enough to wrap the top half inch of the rod.

A small yellow flame that flickers about is not heating the rod properly, however new the rod is. That is a dirty or partly blocked pilot orifice, and the fix is to shut the gas off, take the pilot tube loose and blow it out with compressed air, not to fit another part.

Check 3

The air screen underneath

Heaters made since about 2003 pull their air in through a screen around the bottom of the tank. That screen collects dust, lint and pet hair, and when it blocks, the pilot starves and dies.

Run a vacuum around the whole base. While you are there, move the paint tins, the laundry basket and anything else stacked around it.

Check 4

The thermal switch

Those same heaters have a small switch on the outside of the combustion chamber that cuts the gas if the chamber ever overheats. If it has tripped, no amount of holding the knob will light anything.

On a Bradford White it resets with the red button in its middle, but it tripped for a reason. Something blocked the air or the flue, and that has to be found first, because a blocked flue puts exhaust into the room.

It will not light at all

If you get no flame at all, the question is whether gas is arriving.

Is the gas on? Check the shut off valve on the pipe into the heater and check another gas appliance in the house. A cooker that lights tells you the supply is fine.

Is the igniter sparking? With the light off you can see the spark through the window. No spark and the igniter or its wire has failed, which is a cheap part, and in the meantime some heaters have a lighting hole for a long lighter. If yours is sealed, it does not, and it should not be forced.

New tank, or refilled tank? Air in a new gas line takes a good few clicks to push through. Keep holding and keep clicking for a couple of minutes before giving up.

If it comes down to the gas valve on a heater that is more than ten years old, spend the money on the next heater instead. The tank is the part with a life span, and a new valve on a rusting tank buys you nothing.

Questions people ask

How long can I leave the pilot out?

As long as you like. Nothing is damaged by it. You just have no hot water and, if the house is very cold and the heater sits in an unheated space, keep an eye on the pipes.

Should the pilot really burn all the time?

On a standing pilot heater, yes, that is how it is meant to work. It uses a very small amount of gas. An electronic gas control such as Resideo’s WT8840 keeps the pilot lit too, and opens the main burner only when heat is called for.

It lit and then went out an hour later.

That is usually a draught or the air screen, not the thermocouple. Look for a door or a vent that was opened, and vacuum the base.

Can I change the thermocouple myself?

Yes. Gas off at the valve first, then one nut at the gas valve and a clip at the pilot bracket. Fit the new one with the tip in the same place, hand tight plus a quarter turn, no more. Check every joint with soapy water afterwards and watch for bubbles.

The flame is blue but tiny.

Usually a blocked orifice. Shut the gas, clean the pilot tube with compressed air, and do not poke wire into it, which opens it out and makes the flame worse.

Sources: A.O. Smith "How To Relight A Water Heater's Pilot Light" (waiting, clicking the igniter, thermocouple), Bradford White gas water heater service manual 238-51542-00E (thermocouple and thermopile millivolts, pilot flame, thermal switch, finger tight plus a quarter turn), Rheem use and care manual AP23698 (lighting label) and the Resideo WT8840/WT8860 gas control instructions 34-00013EF (thermopile voltage, standing pilot)