Honeywell Water Heater Status Light: The Blink Codes

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the sources at the end

Honeywell Water Heater Status Light: The Blink Codes

Short answer

The Honeywell gas control on many water heaters has no mains power at all. It runs on electricity made by the pilot flame heating a thermopile, so no light usually means no pilot or a weak thermopile. One blink every three seconds is normal, 2 blinks means the thermopile is low, and a solid light means wait a minute before relighting.

Many gas water heaters, including a lot of A.O. Smith and Bradford White tanks, carry a Honeywell gas control with a small status light on the front. That light tells you almost everything, once you know one surprising fact about it.

The control is not plugged in. It runs on a tiny amount of electricity made by the pilot flame heating a thermopile. No flame means no power, and no power means no light. Everything on this page comes from Resideo’s own installation instructions for the control and from A.O. Smith’s support note on a light that will not blink.

Before you start

What to carry: a torch. Fifteen minutes, and most of it is waiting.

Gas or electric? This is only on gas water heaters. An electric heater has no pilot and no status light: testing an electric heater’s elements.

Find the light. A small light on the front of the gas control, usually near the temperature knob. The codes are printed on a label on the control itself.

Three things before any relighting. Smell gas? Do not light anything. Leave, and call from outside. That comes before this whole page.

No petrol, paint or solvents near the heater. A.O. Smith’s instructions say it plainly: never light the heater with flammable vapours around it.

After a failed try, wait before the next. A.O. Smith says to turn the gas off and wait ten minutes before relighting, and Resideo’s control will not relight while its light is still solid. Rushing it is how people decide a good control is broken.

What the blinks mean

Normal is one blink every three seconds when idle and a quick strobe when heating. Any other count is a code, and it repeats after a three second pause.

Check 1Free, two minutes

Count the blinks after the pause

1 blink every three seconds. Normal. The pilot is lit and the control is waiting. Resideo says this is the control holding the pilot valve open with the main burner off.

A quick strobe every three seconds. Normal. The water is heating and the main burner is on.

2 blinks. Low thermopile voltage, so the main burner will not come on. Check the pilot flame and the thermopile connections.

4 blinks. The water got too hot and the control cut out on its temperature limit. Turn the setting down, and have the control checked if it happens again.

5 blinks. The water temperature sensor has failed.

7 blinks. Resideo calls it an electronics failure: the control is the part.

8 blinks. A warning rather than a failure. The control still sees power with the knob at Off, and Resideo points at the valves.

Solid on. Not a fault. The knob was turned to Off and the control is shutting down. Wait until the light goes out, about a minute, before you relight.

No light at all

The pilot heats the thermopile and the thermopile powers the control. Anything that stops that little chain leaves the light dark.

Check 2

Work down A.O. Smith's list

The pilot is not lit. First on A.O. Smith’s list. Look through the small window near the bottom of the tank. You may need to dim the room lights to see it.

It has not had long enough. A.O. Smith says the thermopile can take up to 90 seconds to get hot enough to power the control after the pilot lights. Keep holding the knob for that long.

Air in the gas line. On a new heater or after gas work, it can take two or three lighting attempts before the pilot stays lit.

No spark. Watch through the window while clicking the igniter. No spark usually means the igniter wire has come out of its connector, or the connector is touching metal.

A tripped thermal switch in the burner area, or loose wiring to the control.

A weak or failed thermopile. Resideo’s test is at least 350 millivolts after five minutes of pilot, measured with a meter. It is a cheap part and the common one to wear out.

Relighting it properly

Check 3Free, ten minutes

Follow the order printed on your heater

Knob to Off, then wait until the status light has gone out completely.

Knob to Pilot, push it in and hold it, and click the igniter button until the pilot lights. Keep holding.

Hold for up to 90 seconds until the light starts blinking once every three seconds, then let go. The pilot should stay lit.

Turn the knob to your temperature. The main burner comes on and the light strobes while it heats: what temperature to set it to.

If the pilot goes out when you let go, the thermopile is not making enough power, and holding it longer will not change that: why a water heater pilot will not stay lit.

Questions people ask

Why does it need 90 seconds when the pilot lights straight away?

The flame lights at once, but the thermopile has to heat up before it makes enough electricity to hold the valve open. Letting go early is a common reason the pilot goes straight back out.

It shows 2 blinks and the pilot is lit.

The pilot is lit but the thermopile is not making enough power for the main burner. A small or yellow pilot flame that does not wrap the thermopile, or a worn thermopile, are the usual causes.

Can I replace the thermopile myself?

On many heaters it comes as a sealed pilot assembly that slides out with the burner. It involves gas fittings and the combustion chamber seal, so follow the maker’s kit instructions exactly or have it fitted.

Is my heater an A.O. Smith or a Honeywell?

Often both. The tank is made by the heater brand, and the gas control on the front is made by Honeywell, now sold under the Resideo name. The codes here belong to the control.

The light blinks normally but there is no hot water.

Then the control is happy and the fault is elsewhere, often the burner not being called for, or a problem downstream of the tank: the order to check a heater that has gone cold.

It went out after the gas was off for work.

Air in the line. Expect two or three attempts, with the ten minute wait between failed ones.

Sources: Resideo WT8840/WT8860 installation instructions 34-00013EF, and A.O. Smith's status light support note