Why Is My Water Heater Flashing a Green Light? Diagnostic Error Codes and Troubleshooting Tips

Discover why your gas water heater is flashing a green light and what it means.

Is your Honeywell or White-Rodgers gas control valve blinking green once, twice, three times, or more?

Should the LED flash green during normal operation?

Learn about the causes, symptoms, and repair tips.

As LED lights on gas water heaters can display various signals, each has a specific meaning. This guide aims to clarify those signals, including the causes and potential repairs. It’s designed for owners of typical gas water heaters found in North America and uses an atmospheric gas water heater from AO Smith as an example.

These heaters come equipped with an advanced gas control valve manufactured by Honeywell.

Gas control valves regulate the delivery of gas to the gas burner. They feature a control knob and an ignitor button for lighting the burner, along with an LED light that indicates the current status or displays an error code (e.g., a flashing green light). Operators can use the control knob to set the desired temperature, including options such as “Low,” “Hot,” and “Vacation” (if available).

The gas valve also includes a thermopile, which generates electricity (measured in millivolts) when exposed to the pilot flame. If the system functions correctly, the gas valve opens to supply gas to the burner. If you suspect the thermopile is malfunctioning, you can test it with a multimeter.

Why Is My Water Heater Showing a Green Light?

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

Solid Green Status Light

If the knob is turned to “OFF,” a solid green light will remain on until the pilot flame goes out. Keep in mind that it may take some time for the thermopile to cool down.

Status Light Blinking

# of Flashes	Status
0	Control Off/Pilot out. LED is not lit. If the status light is not flashing green, try to relight the pilot using our guide or the instructions 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, refer to this article for troubleshooting.
1	Normal 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 from the tap, make sure to turn the knob to “Hot.”
2	Thermopile 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 of any deposits. – Tighten and reinsert electrical connections at the thermal switch and thermopile. – Check the wiring for damage. Replace the thermopile if it shows less than 350 millivolts DC on a multimeter. Condensation may also cause this issue and should clear up as the tank warms.
4	Temperature exceeded. If the status light flashes 4 times every 3 seconds, the pilot light is lit, but the gas control valve has detected high temperatures beyond the limit. The Energy Cut-Off (ECO) activates, shutting down the unit. Call a technician to replace the gas control valve.
5	Temperature sensor failure. If the status light flashes 5 times every 3 seconds, there may be an issue with the sensor. Call a technician to replace the gas control valve.
7	Gas control valve failure. If the LED light blinks 7 times every 3 seconds, the gas control valve has failed. Contact a professional technician to replace it.
8	Power off failure. If the status light flashes 8 times every 3 seconds, the gas valve is OFF, but the thermopile is still generating millivolts. This often occurs when: – The element hasn’t cooled down quickly enough after shutdown. – The control knob is OFF, but the pilot remains lit. You can clear this code by turning the pilot off and relighting it after 10 minutes. If the problem persists, call a technician to inspect and potentially replace the gas control valve.

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 minutes before trying to relight the pilot. If the pilot was lit but the status light still doesn’t blink, check the thermopile or thermal switch, including all connections.

Status Light Is 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.
• Air in the gas line: This often happens with newly installed gas water heaters. It may take several attempts to successfully light the pilot.
• The thermopile is not hot enough or is broken: Ensure the thermopile is fully immersed in the flame. If it still doesn’t work, replace it.
• Gas valve wiring is damaged: Inspect and resolve any wiring issues.
• Loose wire connectors: Ensure all connections are secure and provide full contact.
• Tripped Thermal Cutoff Switch (TCO): If the combustion chamber temperature gets too high, the TCO will trip and cut power to the valve. If equipped with a reset button, reset it. Some TCOs reset automatically. Causes of high temperatures may include flammable vapors entering the chamber, a blocked vent, a dirty filter, or insufficient combustion air.

Why Is My Water Heater Showing a Red Light?

Some water heaters have gas control valves with a red status light, either solid or blinking. For example, Reliance gas water heaters equipped with Honeywell gas control valves use a red status light. Here’s what it indicates:

• Blinking red light (once every 3 seconds): The pilot is lit, and the gas control valve is operating normally. Some models, like Rheem, display a blue light during normal operation.
• Solid red light: The water heater is shutting down.
• Flashing red light (more than once every 3 seconds): This indicates a problem. Refer to the section above on green light blinking for troubleshooting steps.

Note: It may take up to three attempts to light the pilot successfully and see the status light begin blinking, depending on various factors.