Cause 1
Igniter
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.
Cause 2
Pressure Switch
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.
Cause 3
Thermocouple
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.