Have a heater in my shop( colman /evcon ) for 7 - 10 years . New thermostat calls for heat fires up and blower kicks on ,than for about 20 sec, later.. flame goes out, doesn't reset .if I kill the power and than restart system than it will say on all day . Had a professional co. come and replace the control board, limit switch. initiator. Still have no heat Please help john