Lennox Elite furnace stopped firing- need advice

[rfuerst911sc]

Been warm here in GA. the past week so we haven't needed the heat . This morning a little chilly so turned the heat on . I heard the furnace make sounds like it was turning on but no heat . Went into the basement and I see no flame . This is a natural gas furnace. Been working perfect ( to my knowledge ) up until this morning . The gas water heater next to it working fine so I don't believe it is a gas feed issue at least not from the street .
So I'm thinking either the gas is not being triggered to flow or the ignition system is not firing . Not planning on blowing up my house but would like to be able to check a few things on my own . For now I have turned the breaker off to the furnace . Going to be warm here over the next few days so not in crisis mode but it will get colder again so want to get it fixed this week . I do see " lights " on the mother board but have no idea if that's good or bad ?

[flyenby]

On some furnaces there is a test mode, the configuration of lights acts as a self diagnosis

[lonewolf]

yes if the light are flashing there should be a sticker on the inside of the panel where it shows what the flashes mean.

Mine was acting up couple weeks ago , averaging -15c for 6 weeks now
red light flashing twice, meant stuck air valve , couple taps and alls well.

hopefully yours is as easy to figure and fix.

[ledhedsymbols]

Look at this page:

Gas Furnace Sequence Of Operation | RicksDIY.com

Research and find out if your furnace has any special bells and whistles. If not, you should be able to sort out which operation isn't being performed. Do you have a multimeter? Do you know how to use it?

Control voltage is usually 24V AC. Good luck.

[billybek]

As mentioned see if you can read the diagnostic code.

Cycle the power to the furnace to reset and see if it will fire.

This will reset the diagnostic so if you don't look for the combination of flashing leds first it will be cleared. Check the manual or the control panel to see what the diagnostic means.

Pulling the control panel will cycle the power via a door switch and reset the code......

[p911dad]

In my very recent experience with 2 Lennox units, both 15 years old, it could be a number of things. What you really need is a serviceman to diagnose the issue. Our problems were in sequence: the motherboard ($500.) (these things are very much related to computers), the gas valve ($400), or the hard to diagnose igniter. Over 2 years the serviceman replaced the first 2 and cleaned the igniter. They are very much not like the old gas furnaces many of us grew up with, which was basically a thermostat, burner, fan motor, gas valve, limit switch and anticipation switch.
In the last visit, the furnace "clicked" when the thermostat called for heat, but no joy. Turned out the igniter had "carboned over" and shorted it out.

[rfuerst911sc]

I went down to the basement and pulled off the two covers. This is a 2 stage furnace I think . I base that on what looks to me to be two blower motors . One above the combustion chamber and one below. The one above is running constantly when the breaker is on . The one below is not coming on but I would not expect it to because there is no combustion.
I do not see any glowing orange of an igniter or hear any " spark clicking " of an igniter . When I turn off the power, then turn it back on the upper fan comes on and the DS1 red and DS2 green lights on the circuit board both blink in unisyn about every second but after about 5 seconds the red goes off and the green continues to blink every second . Per the diagnostic sticker on the one panel that is either normal or there is something wrong.......gee thanks !
Visually all looks OK so I do believe I have a component failure . I'm not calling anyone today really don't want to pay the Sunday penalty I'll call someone tomorrow .

[billybek]

No clicks other than the combustion fan starting?
I would look at the inducer proving switch first then look for a roll out switch with a manual reset button next. A gentle tapping on the proving switch with the handle of a screw driver might be enough to get it to fire.

[rfuerst911sc]

Originally Posted by billybek

No clicks other than the combustion fan starting?
I would look at the inducer proving switch first then look for a roll out switch with a manual reset button next. A gentle tapping on the proving switch with the handle of a screw driver might be enough to get it to fire.

That is correct just the combustion fan coming on . Actually it seems like the combustion fan is constantly on . There are two tiny switches ( I think they are switches ) that have what appears to be red buttons on them . I will go see if pushing on them or tapping them does anything .

[lonewolf]

If the combustion fan is constantly running it may be trying to go through it 's sequence over and over but something is preventing the firing

google your problem. type in furnace name and what's happening and what lights are flashing.
if you don't have the code breakdown on inside of panel the info is out there somewhere and you will find it.

[rfuerst911sc]

I went downstairs again and started jiggling connections and took a screwdriver and gently tapped various items. I did this with the power off and the service covers off . Turned the power back on , went over to the furnace and manually pushed the safety switch that is activated when the cover is on . The combustion fan came on and after about a minute I saw the glow of the glow plug and then she lit !
I held the button for about another minute and all looked well. Nice blue flame on all four burners. Let go of the safety switch , replaced the cover and now she won't light . So it is either the glow plug or whatever tells the glow plug to come on . Found a local service company that charges the same rate weekends or weekdays for the service call and they are Lennox distributors/installers/repair service . Plus found a 25.00 dollar off coupon so they will show up sometime today.
Decided to go ahead and get it done while I am home vs. having to take time off from work . The furnace was installed in 2006 and I believe this is the first service call ( previous owner had installed ) so not bad . I'll let you know the results.

[lonewolf]

hmmm ,you hold the safety sw and all's well . then you put cover on and she won't lite?
isn't the switch the answer? perhaps the cover is not pressing on it enough.

why don't you rig the switch to stay on and see if furnace goes through a couple on off cycles. if it does then it's the switch.

[rfuerst911sc]

OK the service rep just left and here's the diagnosis . After checking all electrical functions it came down to the portion of the control board that sends voltage to the igniter was only sending a little over 6 volts . So the " rough " price for the control board is 600.00 - 1000.00 . Can't confirm the price until tomorrow. So I tell him to put it all back together.
He puts it back together , hit the power switch and she powers up........ignites and runs ! He let it run for two minutes while he checked a few things then turned off the power switch . Let it stay off for 30 seconds and powered back on and she fired right up !!! He said he believes it is the control board but it is intermittant . I told him to give me a price for the board tomorrow but don't order it yet. So what do you guys think ?

[stevej37]

Just a shot in the dark from here...but did anyone check the condensate line for obstruction? I had the same things happen to mine...they replaced the power board and a few other things before finding a dried up slug in the condensate discharge line. Removed the slug...has run fine since.
Mine would run for about 2-3 min before shutting the gas off.
Oh..I also told them to replace the new parts that they had installed. They weren't real happy with that, but couldn't argue about it.

[lonewolf]

turn it on and let it run and go through a few cycles letting the thermostat turn it on and off
It may be nothing but that switch which is now working.
got nothing to loose

[ledhedsymbols]

I've bought two control boards from Amazon and replaced them myself. Not difficult, and cost me about $100 and an hour of my time. There should be a PN on the board.

[rfuerst911sc]

Condensate line was not checked , on mine it is a clear tube coming out of the condensation tank/pump that goes outside. Visually I see nothing in there that would be obstructing . At this point I will let it cycle a few times on its own tonight and see what happens . I too was thinking about replacing it myself , just a matter of finding the correct board . Thanks guys .

[rick-l]

can you get a part number off the control board?

https://www.hvacpw.com/white-rodgers-21d83m-843-exact-replacement-for-lennox-83m00.html?gdffi=2e782fc658e6478898f8d773e5e17852&gdfms=259B5F83029647CB82D193467F670387&gclid=CjwKEAiA2OzDBRCdqIyIqYaaqQoSJABeJZdiyWED89m4 W6xzM4rNXLoqTsIAX1DUGGspJI8FGFVGkRoCKlzw_wcB

[Por_sha911]

My experience with Lennox was overpriced parts for a crappy product. My biased opinion is do a DIY repair or replace the system with a better product.

[rfuerst911sc]

Been doing some internet surfing to try and get smart . Looks like the original board part number is 100925-02 and is a White Rodgers product . I guess depending on what vendor you go through it has been replaced by 30W25 or 50A66-743 . Both available online for anywhere from 75.00 on up ! Will be interesting what the quote is from the local service company but I have a feeling I will be hanging up with them and ordering/replacing myself . Love this forum !!!