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  1. #1
    Join Date
    Nov 2009
    Location
    Vancouver, BC Canada
    Posts
    19

    Lennox G71 Repeated Vent Calibration?

    I had a brand new G71MPP installed this past Monday and have studying the diagnostic LED (can you say "obsessive compulsive"). I've noticed that when my tstat (Honeywell TH8321U) calls for heat:

    1. It always runs the vent calibration routine as indicated by CAL,
    2. Then the pre-purge/ignition warm up as indicated by blinking a series of flashing H's.
    3. Finally it fires the burners and spins up the blower

    The install manual seems to suggest that vent calibration *may* be initiated by an initial call for heat, and while I have not been able to observe EVERY heating call...I've seen this sequence every time so far. Have other G71 owners observed this? Is it normal?

  2. #2
    Join Date
    Aug 2007
    Location
    louisville, ky
    Posts
    951
    It shouls only calibrate itself the first cycle when its powered up. after that it should run in variable capacity mode. it will show a lower case h if its setup for variable capacity, if not it will show an uppercase H if setup for default mode.

  3. #3
    Join Date
    Aug 2007
    Location
    louisville, ky
    Posts
    951
    Also if it has a venting issue then it will keep trying to calibrate itself.

  4. #4
    Join Date
    Jul 2009
    Location
    Dawson Creek B.C. Canada
    Posts
    24
    The CAL is normal on every heating call. This is just the furnace checking to make sure the venting is free from blockages. You will notice the inducer ramp up in speed then down to a lower speed depending on what the thermostst is calling for.(1st stage heat or 2nd stage heat) This means in variable capacity if the temperature difference in the house is only 1/2 a degree it will start at 40% and ramp up til the heating demand is met. If a setback was used the thermostat is usually calling for 2 or more degrees therefore the 71 starts its cycle at 70% and ramps up till the heating demand is met. The Calibration is due to the ability of the 71mpp to start a low heating stage and vary heating speed according to thermostat demand.(the inducer needs to match the heating speed...ie:40%heating low inducer speed,70%heating med speed, 100% high speed.)
    Hope this makes sense

  5. #5
    Join Date
    Nov 2009
    Posts
    132
    If you have a question such as this, DO NOT hesitate to call the installing company of the furnace. Trust me, they will not think your an idiot or anything like that. They get ALOT dumber questions than this on a regular basis. If you have any questions or concerns about the furnace, you should definately call them, and any decent heating company would have no problem answering questions like this. At least its a halfway technical question and not something stupid like, "I have my thermostat set at 67 why doesnt it ever go above 68?"

  6. #6
    Join Date
    Nov 2009
    Location
    Vancouver, BC Canada
    Posts
    19
    Thanks guys for the responses.

    Who to believe...Vette (who thinks its could represent a venting problem) or tinman (who thinks it should occur on every call?). I need a tie breaker.

    Wisconsin: I hear ya...I have ran the question past my installation company (office manager took the call and will run it past a tech...waiting to hear back)

  7. #7
    Join Date
    Aug 2007
    Location
    louisville, ky
    Posts
    951
    will im looking at my engineering handbook right now and its telling me that it will only display CAL when it is calibrating the high and low pressure switches, after this takes place it will just show a uppercase or lower case h, i could be wrong, i dont see g71's everyday. call your contractor and make sure they set everything up right. should show a lowercase h for variable capcity when the heat is running. if its a capitol h then its not set for variable capacity.

  8. #8
    Join Date
    Nov 2009
    Location
    Vancouver, BC Canada
    Posts
    19
    Quote Originally Posted by Vettgetsmwet04 View Post
    will im looking at my engineering handbook right now and its telling me that it will only display CAL when it is calibrating the high and low pressure switches, after this takes place it will just show a uppercase or lower case h, i could be wrong, i dont see g71's everyday. call your contractor and make sure they set everything up right. should show a lowercase h for variable capcity when the heat is running. if its a capitol h then its not set for variable capacity.
    Almost right. After a CAL, a blinking H = Prepurge/Ignition warm-up

    hxx (input %) pause Axxxx (CFM) = variable capacity
    H1/H2/H3 pause Axxxx (CFM) = staged capacity

    I'm still waiting for a tech to call me back from the company who installed it. I'll update this thread when I hear back.

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    should only calibrate when powered up, not every cycle.

    if you are playing with power or removing blower door it will calibrate every time.
    if going thru calibration on every call for heat you have a problem.

  10. #10
    Join Date
    Nov 2009
    Location
    Vancouver, BC Canada
    Posts
    19
    A tech from the installation company came out today and told me it is completely normal and he's seen it "always" perform a vent calibration on every heating call. I did not believe him based on what the service manual says:

    http://tech.lennoxintl.com/PDFs/0804d.pdf

    He told me that I did not need to be reading the service manual and that I shouldn't need to be watching the diagnostic LED. What an idiot (I figured out that he had more urgent calls and was short handed). I eventually spoke with the local Lennox tech who told me that vent calibration is normal on almost every heating call UNLESS your're running the Lennox Comfortstat 7000. Apparently, with the 7000 connected, the G71 is able to "remember" the vent calibration settings. I'm happy with that answer, and wanted to pass this onto the rest of the forum.

  11. #11
    Join Date
    Aug 2007
    Location
    louisville, ky
    Posts
    951
    the stat dosent have anything to do with the calibration of the furnace, the stat justs sends voltage signals for w1 and w2 for heat output.

    read page 34, it tells u it should only calibrate the first time power is restored by turning the furnace off then back on. or u have a venting issue causing the low pressure switch to open on a call for heat.

    if it keeps calibrating i would bet they went over the eqivelent length of the pvc vents.

    Like i said before, the stat just tells the furnace to come on, and what stage to run, thats all it will do. whether u have a comfortsense 7000, or iaq or vision pro 8000, doesnt matter.

  12. #12
    Join Date
    Aug 2007
    Location
    louisville, ky
    Posts
    951
    when power is restored to the unit the first initial call will run a calibration, then as long as power never goes out, then it will never run a calibration ever again. the in intagrated control board on the furnace remembers the calibration, not the stat.

  13. #13
    Join Date
    Dec 2007
    Posts
    4,710
    Quote Originally Posted by Vettgetsmwet04 View Post
    when power is restored to the unit the first initial call will run a calibration, then as long as power never goes out, then it will never run a calibration ever again. the in intagrated control board on the furnace remembers the calibration, not the stat.

    we are a Lennox dealer and have installed many of these. I will have to disagree and say that I have observed the CAL on most heating calls.

    I was also told that it CAL on EVERY call by tech support and as you stated on every restoration of power.

    conflicting information, who do you trust??

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