Turn off the circuit breaker for the hot water tank. Wait at least 30 minutes for the internal electrical components to cool down. The water in the insulated tank will remain hot, but you will be able to test the igniter system.
Take out the screws in the curved metal access panel near the bottom of the tank then remove the panel. The igniter is inside the tank compartment at the bottom with the flat end pointed toward the gas valve.
Disconnect the back of the igniter from the socket where the two igniter wires are attached to a plastic plug. Do not touch the front tip of the part.
Touch the ohmmeter probes to the two electrical contacts in the plug wired to the igniter. If the display remains at zero or scrolls to the infinity range, the igniter is defective and must be replaced.