If, as Pete suspects, it is a furnace with an intermittent pilot, the flame sensor could also be dirty. When the pilot lights, is there a continuing sound of a spark?
I replaced my blower motor 11 months ago due the original one of 15 years began to make a lot of noise. The replacement shaft had about 1/8" to 1/4" play in it but the squirrel cage wasn't rubbing. Got up this morning to a chilly house and my inducer blower is running but the blower isn't. I now have 10 red flashes on my IFC. This code is "Gas Flow but no call for heat" I have a new blower motor coming from Repair Clinic but do I now have another issue?