Lennox Furnace won't light up

[jeffh]

I wouldn't bother, the furnace should have already been derated for high altitude from the factory. And stick to what the manual says.

[frozenrice]

I have the same furnace as eblend (Lennox G40UH).

I've been having a slightly different problem with ignition of the burners. The furnace comes on like it should, the inducer motor (that helps draw air into the intake) and the main blower fan work (I think), but the igniter doesn't glow so the burner won't light up so all I'm getting is cold air.

LED shows: #1 off and #2 slowly blinking.

I did have a furnace tech come out earlier last week to check on it, and he did some testing and fiddled with connections and it came on. He thinks there was some blockage in the pressure switch line, which is one of the troubleshooting suggestions. All was fine until Friday afternoon/evening when it happened again while I was out. Called the service company and the tech this time said it was either the control board or some loose connections (I wasn't home at the time - SO dealt with it). He managed to get it working again (without a new board), but it crapped out again sometime last night.

I went down to have a look. Same conditions as before, inducer motor but no flame. I went and disconnected the pressure switch hose and reconnected it while the inducer motor was running, and within a minute or so, the igniter glowed followed by the burner lighting up. I'm at work now, but last report was the house was warming up, but I'm not going to place a bet on how long this fix will last though.

I can handle it if it's plug and play, but when it comes to electrical testing, I'm a bit of a lost cause so I'm not confident trying to use a meter to figure things out. I'm debating on if it's the pressure switch or the actual control board. The switch looks to be around $100 and the control board around $225. It'd be nice if I could confidently know which one to try so I don't just arbitrarily throw money at this.

[jeffh]

I suspect the pressure switch. I had a trane tech just detach the tubing to the new trane pressure switch I recently replaced because thats was the only solution they had. He basically bypassed a safety switch because the switches, new and old, weren't working as intended.

[Env-Consultant]

Originally posted by jeffh
I suspect the pressure switch. I had a trane tech just detach the tubing to the new trane pressure switch I recently replaced because thats was the only solution they had. He basically bypassed a safety switch because the switches, new and old, weren't working as intended.

Pressure switch on my end. York - 6 red flashes, high efficiency, 1 year old. Unhooked the tube and held it below to switch - water came out. Shortened the drainage tube so it didn't have 4 bends in it begging for condensation to build up. I also removed the draining going to the pump - cleaned out the sludge in the piping and in the bottom of the pump - all good for the last 3 weeks. Easy fix for $0 - I think the switch is fine and it was just a drainage issue.

[Maxt]

Originally posted by jeffh
I suspect the pressure switch. I had a trane tech just detach the tubing to the new trane pressure switch I recently replaced because thats was the only solution they had. He basically bypassed a safety switch because the switches, new and old, weren't working as intended.

Something sounds really wrong here, high efficiency?

Originally posted by Env-Consultant


Pressure switch on my end. York - 6 red flashes, high efficiency, 1 year old. Unhooked the tube and held it below to switch - water came out. Shortened the drainage tube so it didn't have 4 bends in it begging for condensation to build up. I also removed the draining going to the pump - cleaned out the sludge in the piping and in the bottom of the pump - all good for the last 3 weeks. Easy fix for $0 - I think the switch is fine and it was just a drainage issue.

There was a service bulletin on that, the official fix was to put a pigtail loop in the air switch line, and the pressure sensor line if it was a modulating burner model.

[frozenrice]

Replaced the pressure switch last night and it fired up. unfortunately i woke up this morning to the same thing. inducer and blower working but no flame. LEDs flashing the same code (left=off, right=blinking). Looking more like it's the main board.

[jeffh]

Maxt, if I recall correctly, it was a mid. This was about 6 years ago and I haven't heard anything since. It was a family friend's place

What exactly is a pigtail loop? A spiral of some sort?

[jeffh]

Frozenrice, read the flashes, they are like a morse code of sorts. They will blink a certain amount of times. And that number will translate to a legend on the furnace, usually one of the doors to the cabinet. It is also strange that your blower starts running without gas burning. Note the sequence of operations that it does. Then post it here.

[frozenrice]

jeffh, I was wrong when I said the blower fan was working too. The inducer fan makes enough noise that it sounded as if the main blower was on too. Anyways, after a bit of a gong show yesterday (wrong replacement board was supplied), it seems to be finally working. Woke up to a warm house this morning and just to make sure, I dialed up the thermostat just to get the furnace to fire. It came on like it should so hopefully that was the fix.

As far as I know the codes for Lennox don't have specific number of flashes to diagnose problems. It's either a combination of on/off/quick/slow blinking. As mentioned in my other posts it was one off and the other slow blinking.

[eblend]

Originally posted by frozenrice
jeffh, I was wrong when I said the blower fan was working too. The inducer fan makes enough noise that it sounded as if the main blower was on too. Anyways, after a bit of a gong show yesterday (wrong replacement board was supplied), it seems to be finally working. Woke up to a warm house this morning and just to make sure, I dialed up the thermostat just to get the furnace to fire. It came on like it should so hopefully that was the fix.

As far as I know the codes for Lennox don't have specific number of flashes to diagnose problems. It's either a combination of on/off/quick/slow blinking. As mentioned in my other posts it was one off and the other slow blinking.

Glad you got it working. I am surprised it's the board, unless it has leaking caps or loose connections, I would think they are pretty reliable. I was thinking perhaps it was your igniter. Also, you replaced the pressure switch, but I heard that people say that the actual connection on the inducer fan may be plugged. Have you tried to clean that opening with something? I cleaned mine with just a paper clip, but had no residue of any kind for me. If the pressure switch is not closing, the ignitor would not light up at all. It does sounds like a pressure switch problem, so even if you replaced it, the actual port on the inducer fan may be blocked.

If the issue pops up again, have a look at that connection, and also blow out the tube that makes the connection. Mine was clean but some youtube videos showed definite build up.

[Swank]

I got to join the 'failed furnace' club yesterday. I caught it when the temp only dropped a few degrees in the house. I have the Lennox G60UHV, and the LED was blinking 4-1, same as eblend. Accessing the bolt to remove the flame sensor was a royal pain, but I finally got it. Cleaned it up as best I could with a wet rag, then thoroughly dired it (I read that anything abrasive can cause premature failure requiring a replacement). The furnace ran great all night. I hope that's all it was, time will tell...

Great info in this thread, had I not remembered this I would have called a tech out. Never heard of a flame sensor before, my previous home must have had too old of a furnace or I was just lucky as I never did anything other that replace the air filter in it.

[jeffh]

Pretty much any hot water tank or furnace or gas fireplace has some sort of thermocouple, thermopile or flame sensor to ensure a flame is present. It is an active fail-safe that will shut down the gas valve when no flame is detected.

[dj_rice]

Originally posted by jeffh
Pretty much any hot water tank or furnace or gas fireplace has some sort of thermocouple, thermopile or flame sensor to ensure a flame is present. It is an active fail-safe that will shut down the gas valve when no flame is detected.

So on my old tank, I was having issues with low hot water flow. So I ended up turning the tank off for a a week, bought a new dip tube, Shark Bite connection and repaired it but the pilot wouldn't stay lit. You could light it, but it wouldn't stay lit once pilot button not depressed.


Went to Home Depot and bought a new Honeywell 18" Thermocouple, changed it out. Still wouldn't stay lit. Ended up buying a brand new tank anyway since it was old. Any idea was would of been the fix for that?

New control valve?

[jeffh]

Could be the spring or the small electromagnet that is part of the gas valve assembly.thermocouple coulda been bad, or not in the flame properly, wire from the thermocouple was severed. Or you didnt depress the pilot button enough for the thermocouple to develop a strong enough current hold the gas valve open. I'd assume it was the gas valve, but would inspect things first. Likely a smart bet to just replace the tank, especially if its 8+ years old, than replace the gas valve.

[eblend]

Saw this pop up, and just wanted to give a 2 month updates, since I replaced the gas valve, the furnace hasn't skipped a beat All working great...and overtime with the recent cold snap. I definitely got lucky that it was very mild outside when I was having issues, if it was cold like it has been the last week, I would have just bit the bullet and called a tech to fix that asap.