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  1. #1
    Join Date
    Jan 2003
    Posts
    73

    Unhappy New Lennox Gas Furnace Constant Trips Limit Switch

    Can someone give some idea as what to look for?? As the installer seems to be lost.I had a new House Built last year The General Contractor had a HVAC Contractor install A lennox elite 90 plus propane gas furnace and A/C Unit It appeared to operated fine last winter But This winter it continues to trip the limit switch and the furnace shuts down before the temp is reached in the house I also have a honeywell ditigal set back thermostat installed. Here is what has been done by the installer so far. He has replaced the Limit switch (2) times he has changed the fan speed to operate on high and has also replaced the thermostat this still has not corrected the problem he stated he does no know what else to do.The Thermostat is set to operate at 62 degrees after 11.00 pm at night and back to 68 at 6.00 am I believe the thermostat has some type of memory as to how long it takes the furnace to reach its set temp in the morning The furnace now comes on at about 4.30am trying to reach the 68 degree temp by 6.00 am but as always it reaches approx 66 degrees the the furnace shuts off and I must manually reset it to get to run again.The house also seems to heat very unevenley compared to last year, Any suggestions??? Thanks Dan

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Air flow or over fired.

  3. #3
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,035
    Sounds like something is restricting the air flow across the furnace. Also sounds like your builder's HVAC person has no clue how to figure out what the problem is. If they knew the limit was tripping they should have determined emmediately why it was tripping and fixed the problem. I'm assuming they didn't do this because they replaced it twice and then the thermostat. I'll give them half credit for upping the fan speed only because I'm assuming they did this without having done the measurements listed below before and after doing it.

    Because it's a limit trip there are three primary things they should be checking: 1) air flow across the furnace and total static pressure 2) firing rate of the furnace 3) temperature rise across the furnace

    Either the HVAC company needs to send a more qualified tech out or you need to get another company to look things over.

    You did change the air filter, right? you haven't gone around and shut supply registers off this year or blocked off (with rugs or furniture) return air grills???
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  4. #4
    Join Date
    Feb 2008
    Location
    Western NC
    Posts
    2,504
    Quote Originally Posted by firecontrol View Post
    Sounds like something is restricting the air flow across the furnace. Also sounds like your builder's HVAC person has no clue how to figure out what the problem is. If they knew the limit was tripping they should have determined emmediately why it was tripping and fixed the problem. I'm assuming they didn't do this because they replaced it twice and then the thermostat. I'll give them half credit for upping the fan speed only because I'm assuming they did this without having done the measurements listed below before and after doing it.

    Because it's a limit trip there are three primary things they should be checking: 1) air flow across the furnace and total static pressure 2) firing rate of the furnace 3) temperature rise across the furnace

    Either the HVAC company needs to send a more qualified tech out or you need to get another company to look things over.

    You did change the air filter, right? you haven't gone around and shut supply registers off this year or blocked off (with rugs or furniture) return air grills???
    Yeehaw. Couldn't have said it better myself.

    I agree, you need a new contractor. Any true technician would not accept a bad limit. A limit goes out for a reason. As a service tech, it is their responsibility to find what caused the limit to go out...not stick a new one in and hope it works.

  5. #5
    Join Date
    Jan 2003
    Posts
    73

    lennox limit switch

    Thanks for your reply Yes I change filters every 30 days After 30 days the filters never get dirty but I replace them regardless. I also do not have anything blocking supplies or returns That was one of the first things I checked. One other thing last summer when using the A/C I had to keep wipping up water around the bottom of the furnace. The installer did install a drain but for some reason it will leak water out onto the floor. I do know 1 think for sure since this started the house does not heat as it should sometimes it feels hot in the house other times it feels cold I think that is why they replaced the thermostat I feel since the furnace will not complete a full cycle and stops is why it heats erattic Thanks Dan

  6. #6
    Join Date
    Mar 2008
    Location
    albany, new york
    Posts
    20
    make sure fan is turning, and if so, the right way.

  7. #7
    Join Date
    Dec 2006
    Location
    toronto, canada
    Posts
    551
    Check temperature rise, if it's within the range, i would doubt the board.

  8. #8
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    You really need to get someone out there that knows what they are doing. Sounds more like a ductwork/airflow problem as stated more than a equipment problem. Also when you say standard filter, what brand is it and is it pleated?
    Its a good Life!

  9. #9
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,035
    Quote Originally Posted by dboisel View Post
    Thanks for your reply Yes I change filters every 30 days After 30 days the filters never get dirty but I replace them regardless. I also do not have anything blocking supplies or returns That was one of the first things I checked. One other thing last summer when using the A/C I had to keep wipping up water around the bottom of the furnace. The installer did install a drain but for some reason it will leak water out onto the floor. I do know 1 think for sure since this started the house does not heat as it should sometimes it feels hot in the house other times it feels cold I think that is why they replaced the thermostat I feel since the furnace will not complete a full cycle and stops is why it heats erattic Thanks Dan

    Water anywhere other than dripping out of the drain is a sign of serious problems. Now that you've added this bit of information I will bump up my suggestion to call another HVAC company out to do a full and complete inspection and evaluation to find out what is wrong. At the rate you're having problems you'll be replacing parts and major pieces next!
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  10. #10
    Join Date
    Oct 2002
    Posts
    1,376
    Similiar situation with new home owner job. HO sealed up combustion air vents in furnace closet to tighten his new house. Started tripping on hi limits.

  11. #11
    Join Date
    Dec 2007
    Location
    Kansas
    Posts
    80
    You said propane. Did they convert for it? Call a pro!!!

  12. #12
    Join Date
    Feb 2007
    Posts
    190

    Discharge temp

    Do you know what the discharge air temperature is? Also if your contractor is new to 90% furnaces condensation may be an issue.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,556
    This is a double post of his.
    Much of this was gone over in his other post.

    http://hvac-talk.com/vbb/showthread.php?t=165847
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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