I have a coleman Evcon forced air nat gas furnace. It will cycle or ignite the main burner for 10 seconds and then cycle off. I thought the thermostat was bad so I replaced it the problem still exists. HELP it is getting very frigid and I need the heat.

Not much into coleman,, do they have a flame senser? Look at the diagram pasted to inside of door, should have a parts list and give you an idea where to look for it,, if it has one find remove and clean with fine sandpaper or steelwool,then replace,, seems to be the first thing to try now-a-days