Quick answer
The blinking light on a gas water heater is the status code from the gas control. One flash every three seconds means normal operation. Two flashes mean a weak thermopile, four an over-temperature shut-off, five a temperature sensor fault and seven a failed gas control. No light means the pilot is out. Counts vary by model, so check the label on the tank.
The blinking light on your water heater means the gas control is reporting its status, and the number of flashes between pauses is the message. Count the flashes in one group, wait for the three-second pause, and count again to be sure. The list below is the scheme used on Honeywell electronic gas controls; White-Rodgers controls work on the same count-the-flashes idea, and where the chart on your tank says something different, the chart on the tank is right.
Status light codes on Honeywell and White-Rodgers gas controls
- One flash every 3 seconds: normal. The pilot is lit and the control is working.
- A slow bright-dim pulse, like a heartbeat: normal on Honeywell controls. The thermostat is calling for the burner.
- 2 flashes: weak thermopile. The pilot flame is not generating enough voltage to run the control. More in status light 2 flashes.
- 4 flashes: over-temperature shut-off. The water passed the high limit and the control has locked out. More in status light 4 flashes.
- 5 flashes: sensor fault. The temperature sensor in the tank well is reading open, shorted or out of range.
- 7 flashes: gas valve failure. The control has failed its own internal check.
- 8 flashes, on some Honeywell models: the control still senses a pilot flame after being turned off.
No light at all: pilot out or thermopile not generating
A dark status light means the control has no power. These controls have no cord and no battery: a thermopile sitting in the pilot flame generates the few hundred millivolts that run the electronics. No flame, or a thermopile that has stopped generating, and the light goes out along with the hot water.
- Look through the sight glass at the base for a pilot flame.
- Confirm the gas shut-off on the pipe to the heater is open, handle in line with the pipe, and that other gas appliances work.
- Relight following the label on the tank, holding the knob down until the light starts to blink. The steps are in how to relight a water heater pilot.
- Pilot lights but the status light never starts, or the pilot dies when you release the knob: the thermopile or the control has failed.
Flammable-vapour (FVIR) lockout
Gas tanks built since the mid-2000s are flammable-vapour ignition resistant. The combustion chamber is sealed, air enters through a screen at the base and a flame arrestor, and a thermal switch on the chamber door shuts the gas off if the chamber overheats. Two things trip it: lint and dust choking the air screen so the burner starves, or real vapours from gasoline, solvent or paint thinner igniting inside the chamber.
The result is a pilot that will not stay lit and a dark or faulting status light. If vapours were involved, do not relight: air out the space, remove the source and call. Some thermal switches have a small reset button; others are single-use, and some designs close the air supply permanently, which ends the life of the tank. Vacuuming the air screen at the base is the one maintenance task here that belongs to the homeowner.
Which codes can be reset and which need a new gas control
- Can be relit: no light after a pilot that blew out once, and a 2-flash code after the pilot and air screen have been cleaned. If 2 flashes return, the thermopile is replaced.
- Needs a part, not a reset: 5 flashes. On many models the sensor is a separate plug-in part; on others it comes with the control.
- Needs a technician before any reset: 4 flashes. The lockout does not clear by relighting, and the reason the water overheated has to be found first.
- Needs a new gas control: 7 flashes, and 8 flashes that persist once the pilot has gone cold.
Whether it is safe to keep using the heater follows from the count. One flash and the heartbeat pulse are normal operation. With 2 or 5 flashes the tank is safe but will stop heating, so there is time to book a regular visit. With 4 flashes leave the tank off, because the water has already overheated once. With any code plus a gas smell, leave the house and call Enbridge Gas from outside.
What status-light repairs cost
- Diagnostic visit: $90–$150, applied to the repair when it goes ahead.
- Thermocouple on an older standing-pilot tank with no status light: $150–$300.
- Gas control valve, the fix for 7 flashes: $400–$600.
- Thermopile or temperature sensor: quoted in writing on the visit, inside the $150–$800 repair range.
On a tank over 10 years old, a gas control is worth pricing against a $1,200–$2,500 replacement before you commit. Gas control and pilot work is gas fitting, done in Ontario by a TSSA-licensed technician, and ZK Mechanical's technicians hold that licence. See water heater service, or call (647) 801-1252 or message us with the flash count and the make of the tank.