Hello reppoc. Based on the information you provided, it sounds like the igniter is weak. Test for 3.2-3.6 volts AC at the gas safety valve with the igniter turned on. If the voltage is there, you have a bad safety valve. If the voltage is low or high, you have a weak igniter and the igniter will need to be replaced. You can test this with a multi-meter [AP3873826]. Here is a link on how to use a multi-meter. Hope this helps.
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