I have a 1987 Thermo pride hot air furnace. I have always had it serviced, last winter it started shutting off for no apparent reason. The serviceman came and could not find anything wrong. He did clean it and replaced the filter even though he had done this four months before. It continued to shut off every so often, I push the re-start button and it starts . Now after the blower stops there is quite a low bang in the duct work, I don't know if these two things are related. I would appreciate any advice anyone may have. I just lost my husband and can't afford a new furnace.