Dexter Stack on and off

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Upper level Dexter dryer is heating up on and off, lower level is fine. Checked Computer board, fine, cleaned back of all connection, air swich flip etc. is working.. did call repair person, worked fine when he was here, he left then again on and off heating.. only thing I did noticed that when i did start dryer, igniter trying to ignite , but no luck I did pull up air swich flap, trying again, some times igniting sometimes not.. do you guys think that gas is not coming..don't know.. thanks