Questions tagged [lennox]

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Lennox Wiring for Ecobee SmartThermostat

Confused by the wiring, hope someone can help me out. At the furnace there's only four wires in the cable (R, B, G, and W), but at the other end, a yellow wire appears. It's not reflected in the ...
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31 views

Lennox G40UH erratic behaviour

I've spent the last couple of days troubleshooting my Lennox G40UH furnace. A couple of weeks ago, I noticed that the furnace would sometimes come on briefly (anywhere from one second to a couple of ...
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Lennox 80mgf3-75a-3 furnace 4 flashes of one LED after gas burns, takes forever to heat

I have a Lennox 80mgf3-75a-3. Here is how it is operating: Thermostat sends signal Gas burners come on in about 20 seconds (LED flashes slowly and simultaneously - furnace has only one LED ) Then ...
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How should I troubleshoot a furnace with a possible control board issue?

I have 3 units of furnace in my house (brand: Lennox model: c33-36A-2-6), each cover a floor of my 3-story-house (basement included). The unit covering the 1st floor stopped working a couple days ago, ...
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2 votes
1 answer
117 views

Connecting C-wire to Nest Thermostat for Lennox HVAC

My Nest thermostat has been running fine for quite a while, but recently it started complaining about low battery and wi-fi gets shut down due to power issues. I've been looking for the answer, and I ...
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2 answers
48 views

Lennox gas furnace maintenance

I bought brand new Lennox HE natural gas furnace 3 years back. It has been running perfectly. My dealer recommends to do a preventive maintenance because of 3 years time span. I regularly change the ...
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117 views

Where can I find a replacement limit switch for my furnace?

I had an issue with my furnace. The Fan was running constantly and wouldn't turn off and the heat would not start. Through some research I discovered this was likely due to a fault limit switch in my ...
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1 answer
657 views

Vibrating PVC exhaust pipe from high efficiency furnace

We have a two year old house that has this heating season developed a vibration in the exhaust pipe that can be heard on the first floor of the house. It seems to have decreased as the season has ...
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3 answers
2k views

Updating old Lennox thermostat - wiring confusion

I am trying to update my old Lennox thermostat to a Sensi smart thermostat. I checked the compatibility on the Sensi website and it appears to be a match except for this cluster of wires on the left ...
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Lennox G40UH furnace not turning on

With the lower panel door switch closed, the combustion air inducer comes on. It runs for a little while and then shuts down. Nothing happens in the meantime. The system was working fine until this ...
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200 views

Lennox G12D2E-55C-6 with a Johnson Control G779LHA-1 ignition control and Mercury Thermostat

I am looking to replace the mercury thermostat with a Lux Kono thermostat simply to have the ability to run the fan only and circulate the air. I believe this thermostat does that periodically. I'm in ...
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2 votes
1 answer
4k views

Why is my air conditioner running when the house is below the set temperature?

We recently had a whole new system installed for HVAC. We had a lennox furnace with dehumidifier and UV thing, along with the exterior lennox condenser for A/C. We have the iComfort S30 thermostat, ...
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2 answers
424 views

Lennox G23Q3/4-100-2 And Ecobee4 [closed]

**Pictures attached to go along with my rambling explanation I have my Lennox G23Q3/4-100-2 natural gas furnace and my central air system that has been working since 1995 on a basic programmable ...
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200 views

Is it safe to replace a Furnace pressure switch with one of a different rating? [duplicate]

So I had some problem with my gas furnace and a technician came by to install a new one but it doesn't have the same rating and only has one tube instead of two. He assures me it's fine but I thought ...
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2 votes
2 answers
10k views

Is it safe to replace a Furnace pressure switch with a different one?

So I had some problem with my gas furnace and a technician came by to install a new one but it doesn't have the same rating and only has one tube instead of two. He assures me it's fine but I thought ...
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0 votes
1 answer
2k views

Not able to find Lennox ML193UH furnace filter

I have a Lennox Merit series gas furnace ML193UH in my attic. The furnace turns on, but no air blows out of it. So i figured the filter needs to be changed. But I'm not able to find it. The pictures ...
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-1 votes
1 answer
197 views

Ecobee3 lite connected to Lennox Pulse G14Q Heat/Air Condition

I have read a similar wifi thermo connection feed here and they had success hooking the C wire to the T terminal on the furnace. I can get power to run the thermo from the T terminal, but when I do, ...
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1 vote
3 answers
8k views

How do I connect the spare C wire to the old Lennox system (model # lennox g12q4-110)?

I am trying to install my Ecobee3 now. After finishing the connections, Ecobee did not power up. I did some reading and I believe the C-wire, though it is available is not connected to the power at ...
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1 answer
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Lennox HE propane furnace

I have a Lennox HE propane furnace in the cottage that is set to 41 degrees when we are not there. We head up most weekends and when we get their I boost the temp to 65 deg and get a fire going in the ...
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1 vote
1 answer
983 views

How to set Nest Thermostat to control blower without heat

I have a Lennox G14Q3 propane furnace (forced air). I used the Nest/furnace setup last winter without any problems with just the W and R terminals. But, these summer days I would like to push air ...
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2 answers
337 views

Lennox G16Q3-50 Furnace with AC, Door Interlock Switch and Main Circuit Breaker

If the door of the Lennox G16 is removed, thus the door interlock switch unpressed and system off. Does this mean that I only need to shut off the AC power from the outside breaker panel and leave the ...
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2 votes
1 answer
2k views

How to add C wire to a very old 2-wire Lennox G16 Gas Furnace?

I recently bought a Sensi Thermostat with Wifi to replace my vintage one. I thought it would work with my 2-wire heat only system because it has batteries , but found out that using the Wifi feature ...
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0 votes
0 answers
152 views

Furnace not working

I came home to my furnace having no power even to show trouble codes. I turned off my breaker opened the blower door and it had a blown 5 amp fuse on the curcuit board. I replaced the fuse turned the ...
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1 answer
92 views

What would make my Lennox gas stove just shut off and the pilot light goes out as well?

We've tried cleaning it and restarting the stove still doesn't seem to stay on.
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3 answers
18k views

My lennox furnace has no filter

I searched for 30 minutes, and I could not find the furnace filter, is it possible to install/build a filter slot? my whole family got allergy after turning on heater this winter. Thank you! Lennox ...
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0 votes
1 answer
3k views

What could be causing my Lennox furnace to blow cool air?

My Lennox outside furnace is blowing cool air, not hot even when the burner is lit. It takes 3 times longer to heat the house than it should. I just had the draft motor replace about a month ago and ...
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1 vote
1 answer
7k views

how to change furnace filter (bottom return) for Lennox G43UF

I have a Lennox G43UF furnace and I am not sure if I need to have both a filter for a side return and bottom return. If I do (which sounds logical), where would the location of the bottom return ...
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0 votes
1 answer
10k views

How well does a single A\C unit provide 2 zone cooling?

My 2,900 square foot house currently has two separate AC systems (one upstairs, one downstairs). They're both very old and need to be replaced. One of the four HVAC salesman that provided quotes ...
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1 vote
4 answers
27k views

Why is my Lennox g40uh series furnace not turning on?

I have a Lennox g40uh series furnace and it just stopped working today. I can reset the furnace and can see that on the control board both LEDs (green and red) are blinking together which indicates ...
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8 votes
9 answers
24k views

Where should my furnace filter go in a Lennox G40UHX series furnace?

I have a Lennox G40UH(X) series furnace, which is installed in our attic (We have a single-story house on a slab). Because the furnace is installed in the attic, it is "laying down" on its side, and ...
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