Water Heater Pilot Light Problems

What the pilot light actually does

On a standing-pilot gas water heater, the pilot is a small flame that burns all the time near the bottom of the tank. When the thermostat calls for heat, the gas control valve sends gas to the main burner and the pilot lights it.

Sitting in that pilot flame is a safety sensor, the thermocouple (or a thermopile on many newer heaters). It turns the flame's heat into a tiny voltage that holds the pilot safety valve open. No flame, no voltage, and the valve shuts off the gas. That's the whole point: if the pilot blows out, raw gas doesn't keep pouring into your basement.

Newer heaters with a status light on the gas control tell you the pilot's state directly. On the A.O. Smith ProMax, the light flashes once every three seconds when the pilot is lit, and a solid light means the pilot was lit but is now off.

How to check the pilot light

Look through the small sight glass or viewport near the bottom of the tank, just above the gas control. You're looking for a steady flame wrapped around the tip of the thermocouple. A dark viewport means the pilot is out.

If your heater has a status light, it's quicker to read the light than to squint through the glass. Dim the room lights if you need to; the pilot is small and hard to see in a bright utility room.

Problem 1: the pilot won't light at all

Work through these before you call anyone:

• Gas off at the supply. The manual valve on the gas line to the heater has to be open. If other gas appliances are dead too, the problem is upstream and the gas utility is your call.
• Igniter not sparking. A.O. Smith's manual says to dim the lights and watch through the viewport while you click the igniter button. No spark means checking that the igniter wire is pushed firmly into its connector. Our page on a water heater igniter that isn't working has the full checklist.
• Not holding the knob long enough. The pilot only gets gas while the knob is held in on PILOT. A.O. Smith's procedure has you hold it and click the igniter about once per second for up to 90 seconds.
• Air in a new gas line. After a gas line repair or a new install, it can take a while for gas to reach the pilot.
• Clogged pilot tube. A.O. Smith lists blocked or kinked gas supply tubes as one reason a pilot starves. That's a pro fix.

If the status light still isn't flashing after three tries, A.O. Smith says to turn the knob to OFF and work through the manual's no-hot-water troubleshooting section. If that doesn't sort it out, call a qualified gas tech. Full step-by-step relighting is on how to light a water heater pilot light, and the dedicated pilot light won't light page goes deeper.

Problem 2: it lights, then goes out

A common cause is the thermocouple. If the pilot lights while you hold the knob but dies the moment you let go, the safety circuit isn't seeing enough heat. Either the thermocouple is worn out, it's dirty, its nut at the gas valve is loose, or it's sitting outside the flame.

Other causes from A.O. Smith's list:

• Drafts from an open door or a window near the heater.
• Not enough combustion air, from a cramped closet or a blocked air intake.
• A dirty air filter or flame arrestor at the bottom of the heater. The ProMax manual says a filter that isn't cleaned can let the pilot go out, and says to inspect it at least once a year.
• A failing gas control valve, which usually means a service visit and a new valve.

Start with the cheap stuff. Test the thermocouple before you buy one: see how to test a water heater thermocouple. If it's bad, replacing the thermocouple is one of the cheaper repairs on a gas heater. More detail on this symptom is on pilot light won't stay lit.

Problem 3: weak, yellow or lazy flame

A healthy flame on a gas water heater is blue. A.O. Smith describes a good main burner flame as soft blue, says blue tips with yellow inner cones are fine, and says the flame should not be all yellow. A pilot that's mostly yellow and floppy usually means dirt in the pilot orifice or not enough air.

Lazy yellow flames are more than a nuisance. A.O. Smith warns that poor combustion air can leave fuel unburned and release carbon monoxide, and suggests bringing in a tech to consult on moving the heater. Put a CO alarm near any gas appliance if you don't already have one.

Pilot lit, but still no hot water

If the pilot is burning fine and the water's cold, the pilot isn't your problem. The main burner isn't coming on. That points to the thermostat setting, the gas control valve, or a burner starved of air. A.O. Smith says the gas control valve regulates gas flow to the burner and should be inspected and replaced by a professional if it's defective. See water heater gas control valve problems.

Electronic ignition heaters

Some newer gas heaters have no standing pilot. They use a hot surface igniter that turns on when the heater calls for heat and shuts off once the burner lights. Others light an intermittent pilot with a spark. If one of these won't fire, A.O. Smith's guide says there's no manual fallback when the ignition system fails, so call a pro. Electronic systems can also lock out after several failed tries, which is a safety feature, not a fault.

When to call a plumber, and what it costs

Call a plumber or gas tech when the pilot keeps going out after a new thermocouple, when you see soot or scorch marks around the burner door, or any time you smell gas. A pilot that needs relighting every few days is telling you something.

HomeGuide's figures for common pilot-related repairs:

Many companies also charge a service call fee of $50 to $200. On an old tank, compare the quote with the cost of a new water heater before you approve a valve replacement.