My furnace is natural gas fired. It tries to start up but there is incomplete combustion (yellow flame) and an explosive bang, then a few seconds later it tries again with the same results.
The technician spent all afternoon, did every conceivable test, even on the thermostat and found nothing wrong. I wa ironing clothes in the basement at the time.
He statrted it several times with no problem, then when he went to go with my check in his hand for 170$, I had to call him back again. He still found no faullts, but would be willing to sell me a later model furnace.
I think it may be a low voltage problem, because when I turned the Iron off, it didn't bang. Too it might be a bad batch of gas coming down the pipeline.
I am about to upgrade to 100amp service, perhaps that will help.