Quick answer
4 flashes on a water heater status light means excessive tank temperature: the high-limit cut-out (ECO) has shut the heater down. The code applies to the Honeywell electronic gas control on Bradford White and A. O. Smith-family tanks. It is not safe to keep running. Turn the gas control knob to OFF, do not relight, and call: both manufacturers' charts end in replacing the gas control.
On a water heater status light, 4 flashes means the tank got too hot and the high-limit cut-out shut the gas off. Service manuals call that cut-out the ECO, short for energy cut-off. The chart belongs to the Honeywell electronic gas control used on Bradford White ICON tanks and on A. O. Smith-family tanks, sold in Ontario as John Wood and GSW among others. A different make prints its own chart on the label, and the label on your tank is the one to trust.
Is 4 flashes dangerous? Yes: turn the gas control to OFF
Treat 4 flashes as a stop sign. The ECO is a backstop that acts only after the control's normal temperature regulation has failed to stop the burner. Turn the gas control knob to OFF and leave it there. Do not relight the pilot to get one more tank of hot water.
The water already in the tank is the immediate hazard. Water hot enough to trip the cut-out can scald in a moment, so tell everyone in the house and keep children away from the hot taps. If you must draw water before the tank has cooled, open the cold tap first and add hot slowly. What temperature a water heater should be set to covers normal settings.
The only safe homeowner step on a 4-flash code
- Turn the gas control knob to OFF. The pilot goes out, and that is intended.
- Do not relight, and do not turn the temperature dial down and try again. A lower setting does not repair a control that misread the temperature.
- Leave the temperature and pressure relief valve alone. If its discharge pipe is dripping or has left a puddle, note that for the technician.
- Find out whether the tank is rented. A sticker from Enercare or Reliance means the rental company owns the repair; how to tell if a water heater is rented or owned shows where to look.
What causes the high-limit cut-out to trip
Both manufacturers point at the control, not at anything the homeowner did. Their service literature describes the code this way:
- Bradford White, cause one: a temperature sensor out of calibration. The control believes the water is cooler than it is and keeps the burner on.
- Bradford White, cause two: a faulty gas control. The control fails to shut the burner off at the set temperature.
- A. O. Smith words the same event as “temperature exceeded (ECO activated)” in its service handbook.
Both charts end in the same instruction: replace the gas control. Neither offers a cleaning or an adjustment as the fix, which is why this code is always a service call and never a wait-and-see.
What a technician does, and what a gas control replacement costs
The technician confirms the code, tests the sensor and control against the manufacturer's procedure, and fits the gas control specified for that model. The job involves the gas connection and the pilot and burner connections, followed by a leak test and a check that the burner now shuts off at the set temperature. That is licensed gas work in Ontario, done under a TSSA gas licence.
- Diagnostic visit: $90–$150, credited toward the repair when you go ahead.
- Gas control valve replacement: $400–$600.
- Tank-for-tank replacement, where the heater is old enough that a new control is poor value: $1,200–$2,500 installed.
A workable rule: on a tank under 8 years old, replace the control; past 10 to 12 years, put the money toward a new tank. Hard water in Halton and Hamilton leaves scale in the bottom of a tank, so an older heater here is rarely worth a major part.
Rental tanks: Enercare and Reliance own this repair
If the heater is a rental, do the same first step (knob to OFF) and then call the rental provider, not a contractor. The repair is theirs under the contract, and paying someone else to change a part on their tank can complicate things. Their phone number is on the sticker on the tank jacket.
For an owned tank, ZK Mechanical replaces gas controls and tanks across Burlington, Oakville, Hamilton, Mississauga and Milton; water heater service describes what the visit includes. The Bradford White error code guide lists the other flash counts. Call (647) 801-1252 or book through the contact page, and leave the knob at OFF until a technician has seen it.