Water Heater Blinking Blue Light: What It Means

The Short Answer: A blinking blue light on a gas tank water heater is usually the gas control’s status LED, common on Rheem, Ruud, and Richmond models. A short single flash every few seconds with hot water usually means normal operation. Repeated groups of flashes separated by a pause are a fault code, and what each count means depends on the control, so read your heater’s label.

Normal blink or fault code?

Watch the light for at least 30 seconds.

• Single short flash every few seconds, water hot: usually a “heartbeat” showing the control is powered and idle.
• Light alternating bright and dim: on some controls this means the heater is calling for heat.
• Groups of flashes (for example 2, 4, or 7) separated by a pause: a fault code. Count at least two full groups to be sure.
• No light at all: on a millivolt (thermopile) control this usually means the pilot is out, because the pilot powers the control. See Rheem no status light.

If the light is on an electric water heater’s access door, or on a tankless or heat-pump display, the codes are different again. Flashing green light and 5 flashes on a water heater cover electric status lights.

Why you need your own chart

Rheem-family heaters have used several gas controls, and the same flash count can mean different things on each. One example is Rheem’s technical bulletin 1627 (opens in a new tab) for the PowerVent ESII with Honeywell electronic control. On that control, a short flash every four seconds is idle, but one flash followed by a three-second pause is a low flame-signal warning. Four flashes is a thermal cutoff lockout and seven flashes is a flammable-vapor sensor lockout. Atmospheric (non-power-vent) models with millivolt controls use their own label.

The chart is usually printed on a label on the heater near the gas control or inside the burner access area. Photograph it along with the light. If it is missing, the model number on the rating plate will get you the manual through Rheem’s support page (opens in a new tab).

Common fault groups

Without matching your exact chart, the counts on these controls usually fall into a few families:

For specific counts, see Rheem flashing blue light 7 times and Rheem red light flashing 9 times.

What you can check safely

1. Count the flashes twice and photograph both the light and the code label.
2. Check the area around the heater for gasoline cans, paint, solvents, or a running engine. Move them out and ventilate if you can do so safely.
3. Confirm the gas supply valve is open and other gas appliances work.
4. Reset only as the heater’s label describes. On many models, you turn the control to OFF, wait, and relight following the printed instructions. Do this once.
5. If the same count returns, leave the control off and book service.

What the technician will check

The technician matches the code to your control’s chart and then tests the parts it points to. For a weak pilot or thermopile code, that means the pilot flame and the thermopile output. For over-temperature or vapor-sensor codes, it means the combustion chamber, the flame arrestor, and the sensors, plus a search for whatever triggered the lockout. A gas control is replaced only when the tests point to it, and the replacement must match your heater’s model and gas type.

Frequently Asked Questions

Q: Is a slowly blinking blue light normal? A: On many Rheem-family controls, yes, if it is a single short flash every few seconds and you have hot water. A repeated group of flashes is a fault.

Q: Can I unplug the vapor sensor to get the heater running? A: No. The flammable vapor sensor prevents the burner from lighting when vapors are present. Disconnecting or bypassing it removes that protection and can cause a fire.