The igniters on water heaters tend to be extremely reliable, and if they fail they do not normally do so intermittently in my experience. Make sure the wire is connected at the bottom of the push button that makes the igniter spark. When trying to light the heater be sure to put the gas valve on the water heater in the 'Pilot' position and hold down on the pilot button. While continuing to hold down the pilot button press down on the igniter button three or four times. Repeat this every thirty seconds for two minutes, WITHOUT EVER RELEASING THE PILOT BUTTON. If you have a mirror and the room light is turned off you may be able to see if the pilot light remains lit when you release the pilot button. If not, simply turn the gas valve to the 'On' position and turn the temperature up to the middle of the temperature range (normally represented by a longer notch on the dial). You should hear the main burner light if the water in the heater is not already hot. Adjust the temperature only after you verify that you do not have a (measured) maximum of 120 degrees at your faucet openings after the heater has run sufficiently to cycle the main burner off.