Lennox Furnace not kicking on unless thermostat is turned off then on

sharkbait

Issues with furnace not kicking on…. I have a Lennox G1204E-137-7 furnace and White Rodgers Digital Comfort II thermostat. All will work fine for most of the day or into the night but then at some point it does not kick on. It usually happens at night. I had the cover off to get the model number off the furnace and it kicked on while I was looking inside. Everything looked and sounded fine to my untrained eyes and ears. We can get it to kick on by manually turning the thermostat to OFF, waiting 30-45 seconds and then turning it back on. I replaced the batteries in the thermostat but that did not help. I am tired of waking up cold every morning…any ideas????
Thanks!
Dan

hvactech126

I'm not familiar with that Model number, you may want to recheck it. Usually when turning stat off and then back on you are resetting the control board. Again not being familiar with your model and not know the age I'm unsure if it has a control board. If it does then check the diagnostic lights when it is acting up

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Marty S.

Probably a G12Q4E-137-7. Thirty some year old furnace that should be having annual inspections.

sharkbait

I could have looked at that tag a dozen times and not seen the little tail on the "Q". Yes, you are correct about the model number. The house is close to 30 years old so I am guessing that the furnace is too.

I will take a look for the lights when we have an issue. If I post what the diagnostic lights are showing, will someone here now what it means? I may not be try to fix it but I at least like to be educated when the tech comes to repair it.

Thanks again for the prompt response!

yuri

Has no diagnostic lights, I am a Lennox tech. 95% chance the heat exchanger is cracked at that age. Time for a new furnace IMO. If it is a G12E model the gas valve and damper motor are obsolete.

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sharkbait

If it cycles on and off just fine for the better part of the day, why would you say that the heat exchanger is cracked? Yes it is old but I am not looking for a reason to run out and replace it.....

Hixheat1

Call a pro, it's warmer in the day and the unit runs less. Or your drain line is freezing

yuri

After 30 yrs of expanding and contracting with it being heated and cooled by the flames the metal gets brittle and fatigued and cracked. Google: cracked heat exchanger and hit "Images" to see what happens.

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Marty S.

We say it should be inspected and the heat exchanger is probably cracked because we work on furnaces for a living. We know the heat exchanger on that unit had a 15 year warranty and almost none of them made it 20 years. Cracks in a heat exchanger do not stop the furnace from heating but they do condemn the unit since it's no longer safe to operate. We have no financial gain in this so when the pro's tell you something take it to heart that we're looking out for your best interest.

Hixheat1

He could buy a bird, and teach it to talk. I wonder what it would say? Help I am tired. Listen to the pros.

sharkbait

Understood. I have a tech coming in. My only point was that if I had a 25 year old car and the starter was bad, I could replace the starter. Yes something else would eventually go bad. And yes, I could buy a new car and that would solve the problem too. But before I made the leap to buying a new car, I would do a little due diligence first.

Thanks again to most of you for your help.

Marty S.

Hopefully it all works out good for you . If a new furnace is needed at least you'll recover the cost in fuel savings. I believe the AFUE on that size G12 was only 55% effecient.

beenthere

If you had a 25 year old car. That did the same amount of equivalent work as your furnace has for 25 years. The car would have over 1,000,000 miles on it.

sharkbait

Thanks Marty. The fuel savings will be nice but the upfront cost is a killer. We just spent over 3 grand two weeks ago to have a tankless hot water heater installed and the Christmas bills haven't even hit yet.... The hot water tank was a proactive move because it was old and it would save gas (plus have hot water for my whole family). If the furnace really is that much of an issue, I could have done that first and put off the hot water tank for a year.... Live and learn. Tech comes tomorrow morning so we will see. At least this group has prepared me for the worst....

sharkbait

I don't know if anyone was anxiously awaiting what the tech said........but just in case you were......
Heat exchanger looked fine. Control board is bad and they stopped making them 15 years ago.... Conversion kit would cost a thousand bucks and still leave me with an inefficient, old furnace. So we will be shelling out for a new 95% efficient furnace.

Thanks again for your help guys. Sorry if I was a little defensive but I tend to challenge people and not just take an answer as gospel unless it makes sense to me. And a cracked heat exchanger causing the unit to not fire at night did not seem like a likely issue to me.

Hopefully I will not need to post on here for another 25 or 30 years!