I have a Lennox G60UHV that was installed in Oct of 2005. It is a 2 stage variable, natural gas. We purchased an AC unit 2 yrs ago and it is outside (never a problem with the AC). We have a metal flue pipe so I'm assuming it's and 80+ efficiency.

A month ago on a windy day it started acting up. The furnace ran fine hit thermostat temp and shut down. Then when the call for heat came back on (after it cooled down in the house) it wouldn't turn on. We had to go to the back room and turn it off and back on. Then it would work again for a cycle or two and we'd have to do it again. This happened for a day or so then it worked fine again and we didn't have a problem for another week or so when it got really cold and windy. Same problem. Then a few days ago it started happening again and won't stop. I took the thermostat (Lennox Signature STat) off and replaced it (Lennox Comfort Sense Stat -- under warranty) and thought our problems were over. However last night while checking the new wiring we discovered as the furnace kicked the processes seemed normal... we got to the point where there were big blue flames were blowing and then the LED lights started flashing an error code "Primary, secondary or rollout limit switch open. Limits must close within 3 minutes or unit goes into 1 hour Watchguard"
We got online and read about poor airflow so we removed a screen on the outside of our filter and vacuumed the filter to see if this might be the problem. We turned the power off and back on and then the unit ran without error codes. This morning I woke up and it was only 65 degrees in our house. I upped the thermostat and the stat showed that it was heating but when I went to the furnace room the furnace wasn't running and the LED lights were showing a new code: "Watchguard -- burners failed to ignite; OR limit open more than 3 minutes; OR lost flame sense 5 times in one heating cycle; OR pressure switch opened 5 times in one heating cycle"

We have warranty on parts but not labor so any help is greatly appreciated!

I have a Lennox G60UHV that was installed in Oct of 2005. It is a 2 stage variable, natural gas. We purchased an AC unit 2 yrs ago and it is outside (never a problem with the AC). We have a metal flue pipe so I'm assuming it's and 80+ efficiency.

A month ago on a windy day it started acting up. The furnace ran fine hit thermostat temp and shut down. Then when the call for heat came back on (after it cooled down in the house) it wouldn't turn on. We had to go to the back room and turn it off and back on. Then it would work again for a cycle or two and we'd have to do it again. This happened for a day or so then it worked fine again and we didn't have a problem for another week or so when it got really cold and windy. Same problem. Then a few days ago it started happening again and won't stop. I took the thermostat (Lennox Signature STat) off and replaced it (Lennox Comfort Sense Stat -- under warranty) and thought our problems were over. However last night while checking the new wiring we discovered as the furnace kicked the processes seemed normal....we got to the point where there were big blue flames were blowing and then the LED lights started flashing an error code "Primary, secondary or rollout limit switch open. Limits must close within 3 minutes or unit goes into 1 hour Watchguard"
We got online and read about poor airflow so we removed a screen on the outside of our filter and vacuumed the filter to see if this might be the problem. We turned the power off and back on and then the unit ran without error codes. This morning I woke up and it was only 65 degrees in our house. I upped the thermostat and the stat showed that it was heating but when I went to the furnace room the furnace wasn't running and the LED lights were showing a new code: "Watchguard -- burners failed to ignite; OR limit open more than 3 minutes; OR lost flame sense 5 times in one heating cycle; OR pressure switch opened 5 times in one heating cycle"

We have warranty on parts but not labor so any help is greatly appreciated!!


Clean the flame sensor. That is the cheapest thing to try first.

Thank you. I did that this afternoon as well as change the filter and all seems to be well... for now. However this wasn't a constant problem so only time will tell. Thank you for giving me something to try on my own.

I hope it works out for you.

Worked for me, too. Thanks!!

Seems like a common problem for me. I remembered doing a couple years ago after reading this post tonight. Noticed the house was 5 degrees colder than normal. Check the indicator LEDs and got on Google. Once I saw this post I remembered doing this before. And like last time it worked. 25 below zero outside right now, not a good time to not have heat.

I have an 80 series Concord Furnace, with same symptoms I was making trips into the attic in the middle of the night to reset 'watchguard code' this post has worked for me. I was able to use scotch brite on sensor while still installed. Thanks HVAC1000

Those scotch brite pads are good. They clean it up and don't scratch it up at all just nice and clean. Glad you got it going.

I had a similar problem but my solution was different. When I turned on heat for the first time of the cold season my furnace-G60UHV would not come on.Thermostat showed heat on but no heat. After reading previous posts I was going to clean the flame sensor but it was too hard for me to get to and appeared to be clean anyway from inspecting it visually. After checking other electrical connections and just "feeling around" I noticed that the combustion air inducer motor was hot. This is the motor that draws air up into the flue. I took a small screwdriver and "poked" at the blades on the motor and sure enough it started to turn and the burners fired up and the heat came on. The motor clanked around for a few seconds when starting due to some debris that had somehow gotten into it but then ran OK. I don't know if the debris was leaves or bird nest or some other small critters. While doing all this, I also went through the "unit start-up" procedure several times,but my problem was definely the air inducer motor being clogged up.