Need help..Forced Air Propane Furnace

Discussion in 'Homesteading Questions' started by Qwispea, Dec 3, 2005.

  1. Qwispea

    Qwispea Well-Known Member

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    My furnace isn't heating the house today..it is a propane forced-air furnace..and the burners will not stay lit. My furnace is a Conquest90.. It is high efficiency furnace, 90,000 btu. and 93.5% efficient..new in 1995.

    I tried to trouble shoot myself..thermostat works fine..purge motor works fine..electronic ignitor works fine..burner lits up fine..BUT the burners immediately go out at the precise moment that the blower motor kicks on.


    Again..
    1. thermostat works fine.
    2. purge motor works fine.
    3. electronic ignitor works fine.
    4. burners light up fine.
    5. ..problem area..burners go out at precisely the moment that the blower kicks on.

    I will heat with kerosene this weekend if I cannot figure this problem out..and call the repairman on Monday. But I'd like to do it myself and save from paying a hefty service call.

    Anybody have any experience or suggestions about why the burners would go out at the precise moment the blower kicks on?
     
  2. mpillow

    mpillow Well-Known Member Supporter

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    We had this trouble and ended up replacing the whole gun....I hated that furnace when it was in my house and now that its at camp I hate it when I'm there....10 years ago we switched to HWbb and oil and cut the light bill in half (the fan) and oil much cheaper(halved the monthly fuel) and now we only use furnace for hot water.....and woodstove for heat

    I can sympathize with you....I hated that furnace :grump:
     

  3. mpillow

    mpillow Well-Known Member Supporter

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    My hubby also said you might have a crack ....have your tech check....a crack is bad news, not something you want to live with...okay in a garage if you patch the crack but not for living quarters.......if you can turn the gas off until inspected.
     
  4. Theront

    Theront Well-Known Member

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    My experience with the high efficiency motors is that when the motor starts and the flame shuts down it is the fan. These new furnaces check the fan speed, ours was really dirty. Took it out cleaned it up and reinstalled. The unit then came on and ran normally.
    Theront
     
  5. Cabin Fever

    Cabin Fever Life NRA Member since 1976 Supporter

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    I'm with Therount on this one: check your furnance filter and replace it if it's dirty.

    You can also trouble shoot the problem. Usually on modern furnances there is a little "window" on the outside. Look thru this window is see if there is a light flashing. Count the number of long and short flashes....this is a code. Look the code up in your owner's manual. Sometimes their is a chart right on the furnace with the various codes and things to do to troubleshoot.
     
  6. MaryNY

    MaryNY Well-Known Member

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    No, no!! Sorry I have to disagree with the above, but I don't think it's any of those things. I think it's the thermocouple -- thank goodness I just remembered that word!!! -- I have had it go in gas furnaces I have had - and also in gas water heaters (I think!). Your description is EXACTLY what happens when that thing goes! As I recall it is a little metal thing bent sort of like part of a pretzel that is attached somewhere near the pilot light (I think). It isn't very big, and isn't very expensive to replace, but of course the service bill will be.

    Also, these same sort of problems can occur when the "auxiliary limit switch" goes bad. It also isn't something very expensive, but it also is not something that service reps think of very often. When mine went I went thru two different service companies and it still wasn't fixed. Finally, a friend and his father came over and figured it out and fixed it. It was the father (elderly) who knew what it was. Good luck! Hope you get warmed up and have a nice cozy holiday!

    MaryNY
     
  7. mtman

    mtman Well-Known Member

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    ill go with the limit switch if the fan keeps runnung when the fire goes out i dont think its the thermocouple if that was bad the piolet wouldnt stay lit so it wouldnt go into fire
     
  8. farminghandyman

    farminghandyman Well-Known Member Supporter

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    I just reread, the post BY blower what blower are you talking about, the blower that moves the air through the house? or the exhaust blower for a high efficiency unit?,
    ~~~~~~~~~~~~~~~~~~

    if it is high efficient unit, check to see if there are any obstructions in the vents either the air in or the exhaust

    as there is usually a pressure sensor that checks if there is the proper air flow, and if it is shutting down just as the fan comes on, I would guess it may be sensing either a vacuum or a pressure build up and thus shutting down on the safety circuit,
    ~~~~~~~~~~~~~~~~~~
    I have a lennox pulse unit and if there is a build up in the vents, (birds, frost, and other items) have shut mine down,

    I would guess there is some type of flame sensor that would work like thermocouple that maintains the safety of the system if the flame goes out to shut off the gas, but I do not think a electronic lighting unit uses a thermo couple,
    but if the flame sensor is bad it could be the cause, but I don't think so as it sounds like some thing to do with the forced blower on the exhaust.
    a thermo couple is usually used on a pilot light system and how it works is that when heated it produces some electricity, and that electricity energizes a coil in the valve and holds the gas valve open, (what you are doing by pushing down to light the pilot light button is by passing the thermocouple and as soon as it is generating enough power it holds open the valve and you can then turn it on to main burner,)
    ~~~~~~~~~~~~~~~~~~

    if your talking air circulation blower (fan)

    I would may be check for a loose connection, in the electrical wiring, (the reason I would say this is the circulation blower would pull a lot of amps and if a loose connection is in the circuit, it may pull the volts down enough to shut down the unit, via the control unit) or a cracked burner unit in that the fan is over pressurizing the fire box, some how,
     
  9. farminghandyman

    farminghandyman Well-Known Member Supporter

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    check to see if the blower door is on proper as there is usually a switch that shuts off the unit if the blower panel is removed, it may have got put back on wrong or bumped and when the blower starts it moves the door/panel and the switch is not making contact,shutting it off, (had a furance at church that was not working and it was the panel not put back on correctly).

    the unit does have some form of self diagnosing system on it according to the flyer's, on the net,
     
  10. Qwispea

    Qwispea Well-Known Member

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    First...THANK YOU everybody for your suggestions. This is such a wonderful forum..with many friendly people.


    I finally got the furnace working this evening..and I narrowed it down to a couple of things. Unfortunately..I tried both of these things at the same time so not sure which one was actually the culprit. Usually when I'm troubleshooting like that..I'll only do one thing at a time so that I'll know which action solved the problem..but this time for some reason I did both things before trying it again..

    .........I tried to remove the flame sensor..but it has a 'hook' on the end of it and wouldn't come out..but I think I moved it back and forth enough to perhaps loosen any buildup that might have been on there.
    .........I also connected a green ground wire to the IFC..which hadn't ever been connected before.

    Not sure which one of these did the trick..but it was either the flame sensor or the ground wire.

    Again..THANK YOU to everyone of you. I really do appreciate your concern.
     
  11. Hammer4

    Hammer4 Well-Known Member

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    I'm sure it was the flame sensor. ( Hmm, what do you mean by IFC? )

    There was probably a bad connection or some buildup on the flame sensor and you fixed it by moving it around.

    The burner won't light if the pressure switch that senses air pressure doesn't detect pressure, the burner won't stay lit if the flame sensor doesn't detect flame in a short period of time.

    Anyhow, glad it works!
     
  12. cfabe

    cfabe Well-Known Member

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    Probably the flame sensor. It will probably act up agian at some point. You may want to look into cleaning it well or replacing it. I'm not familiar with your furnace but mine is a 20 year old or so natural gas furnace with an intermittent pilot system, and last year I had to replace the spark ignition controller because it was getting flakey not not detecting that the pilot had light sometimes. I could clean and adjust the sensor, and replace the sensor and it would work okay for a little while, but I ended up replacing the whole control unit. Cost was about $150 for the parts, and not hard to replace.
     
  13. Qwispea

    Qwispea Well-Known Member

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    Yes..my guess would be the flame sensor. And it is cold..so we are very happy its working.

    BTW: I've had troubles with this furnace ever since I bought this home in January 2001. Every year its been something wrong with the furnace..requiring a repairman..paying a service call..

    First it was the ignitor needed replaced.
    Then it was water leaking (high efficiency needs place to eliminate water captured from air)..and the water got some wires wet..and it interfered with wire continuity..and surely I never would have figured that out myself.
    Then it was the inner regulator..needed replaced.
    Then it was the purge motor..plastic fins inside decided to break apart..luckily this I was able to diagnose myself..and I found a replacement in the Graingers for about 20% of retail...
    Then this year the thing wouldn't turn on at all..and the repairman just pushed the motor around one time and that took care of the problem..still cost $80 for service call.
    Now this latest prob..which several people already said..was probably the flame sensor..

    Always something with this furnace..Am seriously going to consider a new one for next year..


    BTW: IFC means Integrated Furnace Control..basically a circut board..that contols all aspects of the furnace.

    Thanks again to all of you who offered suggestions. Mighty appreciated.


    STAY WARM ALL..................