I have a concord 80% efficiency furnace. The fan comes on occasionally but will not stay on for more than a minute. The diagnostic light is flashing a series of 3 lights which indicates a pressure switch or auxiliary limit is stuck open -- how do I find these switches and 'close' them?

Try changing your filter first, and see what happens. If you've already changed the filter, contact a licensed tech. These are both safeties and should be looked at by a licensed trained mechanic, as an unsafe condition exists and the safeties are preventing operation.

Try turning on the fan at the thermostat to determine if the problem is with the fan motor or a control part, with the fan running turn on the heat and see what happens, Good luck, Mike

I have a coleman electric heater where is the limit switch located just installed last feb