My furnace was blowing cold air so I looked the diagnostic light to determine that it was displaying the primary/secondary limit switch open message. Light 1 on 'slow flash' and light 2 'solid ON' .

So after some research I learned that turning off the furnace will reset the limit switch. I turned it off for about 5 hours and upon turning it on it started working.

Unfortunately, it started blowing cold air after 20ish hour of operation and was giving the same message. Turning it off for about 3 hrs has reset the limit switch again and it is running right now.

So my question, is the limit switch the problem? Or do I need to check the inflow and outflow to the furnace? If so how do I inspect the inflow and outflow? I pulled out the filter and it was clean. Must be only couple months old.

I dont know if it is related but around the furnace there was a small puddle of water due to a leak in the washroom. I cleaned it up now. Not sure if that is the culprit.

Also, if the temp dial is set below the room temp then it behaves normally.

Thanks for your help!

 

Check your filter and make sure all the vents are open.

Open the blower compartment and check the fan blades for excessive dust/dirt buildup.

If everything looks good, call for service.

 

Thanks, it's been running fine for a few days now. If it starts giving probs again I will look into your suggestions.