Why my Water Heater is Flashing Green Light? Diagnostic Error Codes and Troubleshooting Tips

Find out why a gas water heater is flashing green light. Do you have a Honeywell or White-Rodgers gas control valve that is blinking green light once, two, three times, or more? Should the LED be flashing green during normal operation? See the causes, symptoms, and repair tips.

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As the LED lights can display differently on a gas water heater, they mean something, and we will try to clarify them for you, including causes and how to repair problems. This article is for owners of the typical gas water heater found in North America, and we will lead you through the process using an atmospheric gas water heater from the AO Smith as an example.

These heaters are equipped with the advanced gas control valve made by Honeywell.

Gas control valves are used to deliver gas to the gas burner. They are equipped with the control knob and ignitor button to light the burner and a LED light showing the current status or an error code (flashing green light). Operators can use control knobs to set the temperature to the desired setting, including “low,” “hot,” and “vacation,” (if applicable).

Gas valves are also equipped with the thermopile designed to generate electricity (in millivolts) when in contact with the pilot flame. If everything works as it should, the gas valve opens to deliver gas to the gas burner. If you suspect that the thermopile is not working correctly, you can always use a multimeter to test it.

My Water Heater Is Showing Green Light – What Does It Mean?

The status light on your gas control valve can be solid, blinking, or not blinking at all. Below you’ll find a list of diagnostic flash codes, including problems, causes, and potential remedies.

The Status Light Is Solid

If the knob is turned OFF, you will see a solid light until the pilot is out. Note that it takes some time before the thermopile cools down.

Status Light Blinking

# of FlashesStatus
0Control Off/Pilot outLED is not lit. If the status light is not flashing green, try to relight the pilot using our guide or instructions found on the heater’s label. Look through the heater’s viewport at the bottom of the unit to ensure that the pilot is ON. If there are any issues with the pilot, use this article to troubleshoot it.
1Normal operation. If the status light flashes once every 3 seconds, the pilot is lit, and the gas valve operates normally. If there is no hot water coming out the tap, make sure to turn the knob to “hot.”
2Thermopile voltage low. If the status light flashes 2 times every 3 seconds, the pilot light is on, but the thermopile doesn’t generate enough millivolts to keep the gas valve open.Before replacing a weak or broken thermopile or calling a technician, clean the thermopile from deposits, tighten, and reinsert electrical connections at the thermal switch and thermopile. Also, make sure that the wiring is not damaged. Replace the thermopile if it shows less than 350 millivolts DC on the multimeter.Condensation can also be the cause of this problem and would clear up as the tank warms up.
4Temperature exceeded. With the 4 flashes every 3 seconds, the pilot light is lit, but the gas control valve has detected high temperatures that exceed the limit. In this case, the Energy Cut Off-ECO gets activated, shutting down the unit. Call a technician to replace a gas control valve.
5Temperature sensor failure. If your water heater flashes green 5 times every 3 seconds, you might have a problem with a sensor. Call a technician to replace a gas control valve.
7Gas control valve failure. If the LED light blinks 7 times every 3 seconds, you have a problem with a gas valve. This one requires you to contact a professional technician to replace a gas control valve.
8Power off failure. Eight flashes every 3 seconds means that the gas valve is OFF, but the thermopile still produces millivolts. This often happens when the element doesn’t cool down quickly enough after the unit shuts off. It can also occur when the control knob is OFF but the pilot is still running. You can clear this code by turning the pilot off and relighting after 10 minutes. Call a technician to check your gas control valve as it might need replacement.

Note: The status light begins to blink when you light the pilot. If it doesn’t flash green after a minute or two, stop and wait at least 10 min before trying to relight the pilot again. And if the pilot was lit, but the status light doesn’t blink, make sure to check the thermopile or thermal switch, including connections.

Status Light Not Blinking

There are several reasons why the status light on your gas control valve is not blinking:

  • The pilot is not lit. Follow the instructions found in our article on how to light the pilot properly.
  • There is air in the gas line. This usually applies to newly installed gas water heaters. It may take you several tries before lighting the pilot successfully.
  • The thermopile is not hot enough or is broken. Make sure that the thermopile is fully immersed into the flame and if it still doesn’t work, replace it.
  • Gas valve wiring is damaged. Make sure to correct the issue.
  • Wire connectors are loose. Ensure that all connections are tight to provide full contact.
  • Tripped Thermal Cutoff Switch – TCO. When there is an extremely high temperature inside the combustion chamber, the TCO will trip and cut power to the valve. If it comes with the reset button, then you can reset it. Some will also reset automatically. The reasons for the high temperature inside the combustion chamber might be the released flammable vapors from the outside, blocked vent, dirty filter, and insufficient combustion air.

My Water Heater Is Showing Red Light – What Does It Mean?

Some water heaters include gas control valves with the red status light, either solid or blinking. For example, Reliance gas water heater is equipped with the Honeywell gas control valves with the red status light, and here is, in short, the meaning:

  • The red status light blinks once every 3 seconds when the pilot is lit, and a gas control valve operates normally. Some water heaters, such as Rheem, display blue color during normal operation.
  • Solid red status light means that the water heater is shutting down.
  • If the red status light flashes more than once every 3 seconds, there is a problem. Check out the solution in the above text about green light blinking.

Note that sometimes due to various reasons, it may take up to 3 attempts to light the pilot, and you see the status light blinking.

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