Water Heater Not Lighting

Some water heaters use an igniter to ignite the gas. If the igniter fails, the burner will not light. To determine if the igniter is defective, first make sure the igniter is getting voltage. If the igniter is getting voltage, but it doesn’t glow, this indicates that the igniter is defective and should be replaced.

The draft inducer fan motor draws air into the burner and then exhausts it out the flue. As the air flows through the draft inducer assembly, it closes a vacuum switch to signal that proper air flow is present. If the inducer motor is not working properly, the water heater's burner won't light. Over time, the bearings on the inducer motor wear out. The inducer motor could also have a clogged vacuum port. If the vacuum port is clogged, the motor will not be able to close the vacuum switch, preventing the ignition process from continuing.

The pressure switch closes when the proper airflow is achieved, signaling the control board to continue the ignition process. If the pressure switch is defective, the ignition process will stall, and the water heater will not light.

The thermocouple detects the pilot flame. If the thermocouple does not detect a flame, the ignition process will stall, and the burner will not light.

Most limit switches are resettable. If the limit switch or thermostat has a reset button on the back you should be able to reset it. If the button is popped out the limit switch or thermostat has tripped. You can try resetting it by pressing the button. You should hear a click when it resets. You can check the limit switch or thermostat for electrical continuity with a mutimeter.

When the main burner lights the gas valve senses the flame through the flame sensor. If the main burner will not stay lit the flame sensor may be dirty or damaged and will need to be replaced. Most flame sensors are part of the igniter assembly and are not sold separately.

The pilot ignites the water heater’s gas burner. If the pilot does not light, the water heater will not heat. Sometimes, carbon deposits can build up on the pilot and eventually create a restriction. If the pilot is restricted, try removing it and clearing it with a stiff brush and/or compressed air. If the pilot cannot be cleaned, replace it.

Some water heaters use a spark electrode to light the pilot flame. The spark electrode sends intermittent high-voltage sparks to light the pilot. If the spark electrode won’t produce sparks, it is likely defective. If the spark electrode is defective, replace it.