How to Repair a Water Heater That Won't Stay Lit or Keeps Turning Off

If your gas water heater doesn’t stay lit, you may have a defective thermocouple. Most gas fired water heaters use a standing pilot to ignite the main burner. The gas for the pilot assembly is supplied by the main gas valve and is monitored by the thermocouple. The thermocouple is a heat sensing probe that is part of the pilot assembly and sits just above the pilot flame. When the pilot light is functioning properly, the thermocouple will generate a small voltage that is fed back to the gas valve to keep the gas flowing to the pilot light. If the thermocouple is defective, it will not sense the flame and the gas valve will not receive the proper voltage signal to keep gas flowing to the pilot assembly. The thermocouple probe sits in the pilot flame continuously and will eventually burn out. Testing the thermocouple requires special test equipment and therefore replacing it is usually the most practical method of troubleshooting. Verify that the pilot flame is clean and contacts the end of the probe fully before condemning the thermocouple. Changing the thermocouple does not involve any gas fittings but local regulations may require that a qualified gas technician perform the repair.

If your gas water heater doesn’t stay lit, you may have a defective control thermostat. This control is part of the gas valve assembly and normally has a dial that will allow for temperature adjustment and will also have a probe that monitors the water temperature. The gas supply to the pilot assembly is controlled by this valve. If the pilot light won’t stay lit and the thermocouple is okay, then the thermostatic control valve may be defective. Replacement of this part should be performed by a trained gas technician.