The part(s) or condition(s) listed below for the symptom Water heater not lighting are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
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 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.
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.