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is the flashing light constant with a slow blink? And not in groups?
Thank you...does your thermostat require batteries?
A slow blink = normal no call for heat..
Thank you...and does the exhaust fan start?
Can you feel the exhaust fan when the furnace is blinking, thermostat turned to heat and turned up....and tell me if warm?
Thank you...last question...
If you turn unit off by main power and turn back on 20 seconds later..does the furnace go directly to continuous flashing?
Ok, you have a bad circuit board.
If there is a failure like pressure switch, limit, flame sense the furnace at least goes through start up and then faults.
Yours is faulting before a trial...you have a bad circuit board.
If you need anything else let me know. After service is rated at top of page you have 30 days of followup
on furnace circuit board where thermostat wires attach. Use a short wire shaped in a U and hold one end on R and other on W.