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Lennox furnance model G20 won't come on

Discussion in 'After Hours Lounge (Off Topic)' started by Jason Kirkpatri, Sep 16, 2006.

  1. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    Hi all,

    I've tried everthing that I can think of, but my furnance just won't come on! It's a "Whisper Quiet" Model G20. I've turned off the gas flow, power, and thermostat and turned everything back on (after 5 minutes) with the thermostat cranked to 90 degrees. Still won't come on. I've checked the lower panel and the safety switch is being depressed correctly with the panel installed.

    Any thoughts? I have the Honeywell ingnitor and as far as I know, it's an electric starter, meaning that there isn't a pilot light that runs continously.

    Thanks in advance for any insights!
     
  2. DougR

    DougR Well-Known Member

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    Do you have just Standard Thermostat? Or Combo Heating/Cooling ? Make sure it's set in the Heating Mode?

    The Fan doesn't come on at all?
    Did you try Depressing the Panel Safety Switch with the Panel Removed ?
    See if there is a Fuse on the Control Panel inside, may be Blown ?

    Does it give any kind of Code ( Blinking Light on Circuit Board) ?
     
  3. johnADA

    johnADA Well-Known Member

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    OK, if the unit tries to come on, pre ignition blower fan, then its probably not seeing a flame and shutting down.
    Stupid trick, but works great for high eff, furnaces made today. Just in front of the flame path you'll see a thin wire, its called a flame sensor. Take it out and wipe it down good with a dollar bill, yes a dollar bill, you dont want to break through the plating. What happens is carbon builds up very thinly and it wont see the flame for the breif period its on for.

    If it doesnt even start at all, remove the thermostat and tie both leads of the wires together and see if it runs then.That shows if the stat is bad since its taken out and out on full run.

    Neither are it, post back!!
     
  4. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    Just got home - will give said advice a shot!
     
  5. Eric Kahn

    Eric Kahn Guest

    The other thing to check if the fan comes on but never goes to flame is the pressure differential switch (looks like a 2 to 3 inch black pancake) or the fan might have a centrifical switch if there is no pressure diff switch

    if the vent fan does not come on, stick somthing in to it and see if you can turn it alittle, I had to do that last year to get it to work the first time and it worked fine after that
     
  6. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    Hopefully the pictures turns out and isn't too large (flash is on the fritz). I can hear the gas coming on, but no ingnition. I think that the carbon buildup sounds like a good path to pursue...but I have no idea where to look. It's probably behind the damper door and if so, that's a bit beyond me.

    I checked the fuse on the lower panel - all good. Checked the pancake safety switch - all good. I didn't try the thermostat bypass because I'm assuming that since I can hear the woosh of gas, that the thermostat is working. The fan is in a self-contained unit so no spinning the blades for me. [​IMG]

    I've found the manual online and it says that you are not to manually attempt to try to light the pilot yourself, this being an automatic ignitor.

    I'm off to bed and I'll check back tomorrow, but I think I might end up calling somebody in.

    Thanks for the kind advice and taking the time to help a fellow out!

    Jason

    [​IMG]
     
  7. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    -double post-
     
  8. johnADA

    johnADA Well-Known Member

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    Find your owners manual. It will show a layout in it, showing the location of the flame sensor.Not seeing your exact model, but knowing others, you'll see where the gas tubes run under the exchanger.There is usually a simple 2-6 screw cover over it with a gap under it. Remove that cover and the snesor will sit in the path of one of the gas tube ends. 1/16th in diameter or so with a single wire connector on it also held into place with one screw.
    Dollar bill works the best for average people, but super fine steel wool with 2 strokes tops works the best. Remember you dont want to scuff it, just remove the deposits!!
     
  9. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    I've tore the house apart looking for the manual [​IMG]. Still in search mode so hopefully it turns up. I can see where the gas comes in to the exchanger so I'll have a look there.

    Thanks, again!
     
  10. Eric Kahn

    Eric Kahn Guest

    you need a new ignitor, if you here gas coming on but no flame it usually means the ignitor is bad, now all you have to do is find out if it is a hot surface ignitor or a spark ignitor, hot surface ignitors tend to fail the first time you call for heat after a long off period
     
  11. DwightK

    DwightK Well-Known Member

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    I had a similar issue and the gasman showed me that in the pilot tube there is a small hole (usually on the backside so you can't see it) that can sometimes get clogged with lint or somesuch. If the pilot won't stay lit this is the cheapist thing to check for.
     
  12. johnADA

    johnADA Well-Known Member

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    Ok, first off he has a newer furnace which most are energy efficient and dont have pilots.

    Ok, you can also once you've removed this cover panel, find the cover limit switch. Usually a push button type deal near the sides of the door. You can push that in and have the stat turned up so let it run through its paces.

    All newer ones will go through this similar scenario you can listen for.First it'll click on, you'll see a LED light on the mini processor. Then after it clicks on a 1 or 2 stage mini blower will come on to clean out the furnace passages of bad air etc.If that doesnt happen , then one of the pressure switches might have gone bad or the mini processor internal switch is bad.

    If the blower starts you then watch the ignition area at the ends of the gas tubes.The igniter no matter the kind will be turned on and begin to glow. It if doesnt get bright red and extremely hot it wont light, the flame sensor wont pick up flame and shut the unit down.Again could be the mini processor, but this you can check 2 ways. Ohms for complete circuit, or voltage readings. If it gets either, the ignitor is bad. If it doesnt, processor could be bad.

    If it glows and lights but immediately shuts down which has the highest occurrence rating for your problem, the flame sensor is caked,which we went through.

    I'm not a furnace repairman by any means, but I could run with the best of them since I dont believe in repair persons for most anything since I'm a millwright and our job is to fix anything!! Jack of all, master, so they say, of none!!

    Google searches can help for manuals. Manuals should have a jacket and attached to such items for these times. And google comes up with these for DIYers and more if you search

    http://hometips.com/home_probsolver/...forcedair.html
     
  13. johnADA

    johnADA Well-Known Member

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  14. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    I am literally jumping up and down! Fixed! Great links - thanks so much!

    I removed the lower panel and pulled out the inside metal "cup" to put more pressure on the safety switch when installed. This seems to have done the trick as when I powered it back up, the damper door came down (scared the shit out of me) and we're up and away!

    I'm still concerned as I don't 100% know if I "fixed" anything or not. We're hovering around 40 degrees for the next week so if something is screwed, it should show itself.

    Thanks again guys!! Where else would I go other than HTF for advice on my furnace? [​IMG]
     
  15. DougR

    DougR Well-Known Member

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    [​IMG]

    Sometimes it needs a Little Tweaking !!
     
  16. johnADA

    johnADA Well-Known Member

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    Should make this a sticky for DIY furnace repair!!!!!
     
  17. DougR

    DougR Well-Known Member

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    It's getting close that time of year for some of us !! [​IMG]
     
  18. Eric Kahn

    Eric Kahn Guest

    Can't be a DIY repair with the use of the BFH (Big FreakING hammer)[​IMG]
     
  19. Jason Kirkpatri

    Jason Kirkpatri Well-Known Member

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    I was tempted. If it wasn't for that stuff called "gas", there may have been some fine tuning followed by complete rampage. Luckily, it never made it that far!
     
  20. johnADA

    johnADA Well-Known Member

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    Yes it is and mines allready run for one night, well tried too and I allready have my first fix of it.

    Wife turned it on to take the chill out of the air and it didnt fire, but did she tell me that. he next day I hear this hum I cant at first figure out where its coming from. Its the furnace, draft motor wont come on and its HOT. A little baby bird fell into the stack and got wedged in the motor blades stopping the motor, wouldnt let it light.
    I was like, here we go again!!!
    Since we got this house with then a 2 year old Trane, its been nothing but problems, which I had hoped were fixed. One processor unit, one igniter, water drain problem and 3 times the flame sensor needed cleaning. They say you cant stop a Trane, little bird didnt have a problem and this Trane in 10 years since doesnt seem like it wants to go!!
    I think the 85% eff. rating means the amount of time during its life span it runs!!!
     

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