The igniter is supposed to light the burner automatically, whenever a hot water faucet is opened. If it does'nt, check to see if there's a spark between it and the burner at all. If there is, it should a bright blue color. If it is'nt, adjust the spark gap to produce one. If it is, try to light the burner with a flame, and, if it does'nt light, replace the gas valve.
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