musicis

Hello....I fired up my ~ 10 year old furnace just today for the first time this cold season and got consistent cold air blowing out the vents. The control panel is flashing 4 times and then a pause. I found a pdf form that says this about the error message:

"4 RED FLASHES: This indicates that a primary or auxiliary limit switch has opened its normally closed contacts. The control will operate the supply air blower and inducer. This condition may be caused by: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor. Also, this fault code could be caused by a blown fuse located on the control board."

I checked the fuse and its good. I checked the Primary and auxiliary contacts with no power on the furnace and continuity was there. I assume the contact breaks when the system starts? Filter is new. Blower seems good. Any help on this would be great. Model g8t08012dna11a serial wdlm003595

Thanks in advance for any help.

glennjanie

Welcome Musicis:
It appears you have covered most of the trouble-shooting items. We know it has worked for 10 years with the duct, blower speed, same blower motor and firing rate. Now, we must decide which of these items has changed; check for obstructions in the duct, or too many registers blocked or turned off, we don't have a firing rate because we are blowing cold air.
It may help to do some cleaning on the furnace. Spiders love to build little nests in the pilot tube, the openings of the burners and other places. If it is a standing pilot, is it burning? or is the hot surface ignitor heating up? Do the burners come on at all? If it is a standing pilot, I would check the thermocouple.
We are still open to further information or questions, and please let us know how it works out for you.
Glenn

kok328

replace the bad limit switch.