High Limit Switch - Page 2
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  1. #14
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by MikeJ
    Sounds similar to a problem I ran into once. Took awhile for me to realize that when only one zone was calling, there was not enough air flow and the limit would trip (open), causing the burners to shut off and the blower to run until the unit cooled down. Then it would relight just after the blower quit and run for a bit and do the same thing. I opened both zones and didn't have this happen so I deduced that one zone only was too restrictive.

    Try keeping both zones calling with a setting of 80 or so. Open your windows and see if the unit will continue to run. Or if you can, manually open both zones.

    Another thing is set an appointment with a better company or the utility but let the house cool to a low temp., Then when the tech gets there let him up the temp and see what happens with only one zone calling. Just a thought.
    From August 2000 until December 2004 the unit worked flawlessly. Jan/Feb 2005 the problems started. And while I'm typing it's happening again...I had to reset the unit.

  2. #15
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    You also need to have the gas pressure checked at the manifold.

  3. #16
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by beenthere
    It might be going into a soft lock out.

    Are your zones the same size, or is one alot smaller then the other.

    Does it have a bypass.

    Your evap coil may be dirty and causing the limit to do its job.
    Two story colonial, ground floor is one zone, and upstairs is the other zone, floor space of approximately equal size...when one zone opens the other closes, so that at the end of a heating cycle, if the other zone isn't calling for heat, the dampers are open. BTW, I'm seriously considering having the coil cleaned (cost - $XXX).

    (No pricing, due to site rules )

    [Edited by jultzya on 10-29-2005 at 01:53 AM]

  4. #17
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by beenthere
    It might be going into a soft lock out.

    Are your zones the same size, or is one alot smaller then the other.

    Does it have a bypass.

    Your evap coil may be dirty and causing the limit to do its job.
    Mr. Been: I've been rereading all the posts/responses to my question. What I want to make clear, and I'd appreciate your input on this, is that I'm not saying that the limit switch isn't doing what it's supposed to do. What I'm saying is that the limit switch won't let go, in effect, of the blower. It shuts down the burners like it's supposed to do, but the blower keeps going even after the heat exchanger has cooled down. That is what I'm questioning. The limit switch does what limit switches are designed to do, but why won't it let go even after the unit has cooled down?

  5. #18
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,377
    Eapples
    The limit switch is doing what its supposed to do. Shutting down the burners when the chamber gets to hot. This switch is a manual reset. When you turn off the stat or the power to the control board it resets. If this limit trips as you say then you have a lack of air flow.

    You need to get someone out that knows that furnace and the zone system.
    Call your utility back, Let them check all the supply registers in the house zone by zone.This is what your paying for let them fix it or they can pay for someone that can.

  6. #19
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by pecmsg
    Eapples
    The limit switch is doing what its supposed to do. Shutting down the burners when the chamber gets to hot. This switch is a manual reset. When you turn off the stat or the power to the control board it resets. If this limit trips as you say then you have a lack of air flow.

    You need to get someone out that knows that furnace and the zone system.
    Call your utility back, Let them check all the supply registers in the house zone by zone.This is what your paying for let them fix it or they can pay for someone that can.
    Mr. Pec: Thanks for your input. My mo with the utility is to keep calling them back to fix the problem, figuring that at some point they'll actually do something to fix the problem. Just one thing, though...the furnace worked with absolutely no problem for almost five years. Why would it start acting up now? I figure that the system was designed to work with the zoning system that I have, and that the only logical reason for the malfunction would be restricted air flow, as so many have pointed out, caused by a dirty coil. Unless I'm missing something, I don't understand how the zoning system itself could be contributing to the problem.

  7. #20
    Despite what some folks say there are coded that show when the limit opens.

    I would suggest on the face of it that the thermo

  8. #21
    Originally posted by curry
    Despite what some folks say there are coded that show when the limit opens.

    I would suggest on the face of it that the thermostat might be of the energy robbing type if it is electronic or you could have a an issue with duct work .

    That is the short version but could go much deeper than that. Have a complete check out.

  9. #22
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by curry
    Originally posted by curry
    Despite what some folks say there are coded that show when the limit opens.

    I would suggest on the face of it that the thermostat might be of the energy robbing type if it is electronic or you could have a an issue with duct work .

    That is the short version but could go much deeper than that. Have a complete check out.
    Mr. Curry: The fault indicator on the furnace indicates that there's a problem with the limit switch. Regarding your other comments, the thermostats are digital, with the downstairs one being the "master", and the upstairs one being the "slave", i.e., upstairs works off batteries and defaults to the setting of the downstairs one (heating/cooling), while the downstairs one is hardwired. Also, about the ductwork...these problems didn't happen when we moved in to the house in 2000. They're only happening now, so I don't understand how the ducts could be the problem...wouldn't this problem have shown up sooner? Nevertheless, I appreciate your input. Thanks again for your help.

  10. #23
    Join Date
    Jun 2005
    Posts
    169
    Originally posted by eapples
    What I want to make clear, and I'd appreciate your input on this, is that I'm not saying that the limit switch isn't doing what it's supposed to do. What I'm saying is that the limit switch won't let go, in effect, of the blower. It shuts down the burners like it's supposed to do, but the blower keeps going even after the heat exchanger has cooled down. That is what I'm questioning. The limit switch does what limit switches are designed to do, but why won't it let go even after the unit has cooled down? [/B]
    THE FUNCTION OF THE LIMIT SWITCH IS TO SHUT DOWN THE GAS VALVE BECAUSE THE HEAT EXCHANGER IS GETTING TOO HOT. THE
    BLOWER CONTINUES TO RUN TO HELP IT TO COOL DOWN. IN LATER
    MODEL THE FAN/BLOWER IS CONTROL BY TIMER INSTEAD OF TEMPERATURE CONTROL.

  11. #24
    Join Date
    Nov 2004
    Location
    Michigan, Detroit Metro area
    Posts
    296
    quote:
    --------------------------------------------------------------------------------
    Originally posted by eapples
    What I want to make clear, and I'd appreciate your input on this, is that I'm not saying that the limit switch isn't doing what it's supposed to do. What I'm saying is that the limit switch won't let go, in effect, of the blower. It shuts down the burners like it's supposed to do, but the blower keeps going even after the heat exchanger has cooled down. That is what I'm questioning. The limit switch does what limit switches are designed to do, but why won't it let go even after the unit has cooled down?
    --------------------------------------------------------------------------------

    It is a design feature to draw attention to the fact that the furnace is malfunctioning.


    What's my post count now?
    UA Local 636

  12. #25
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by rohalon
    quote:
    --------------------------------------------------------------------------------
    Originally posted by eapples
    What I want to make clear, and I'd appreciate your input on this, is that I'm not saying that the limit switch isn't doing what it's supposed to do. What I'm saying is that the limit switch won't let go, in effect, of the blower. It shuts down the burners like it's supposed to do, but the blower keeps going even after the heat exchanger has cooled down. That is what I'm questioning. The limit switch does what limit switches are designed to do, but why won't it let go even after the unit has cooled down?
    --------------------------------------------------------------------------------

    It is a design feature to draw attention to the fact that the furnace is malfunctioning.


    Mr. Rohalon: Unless one of the pros in this forum says you're wrong, I'd say your answer makes sense. What all the suggestions/recommendations are pointing to is that I should start somewhere, e.g., with getting the coil cleaned. If the problem persists, and the utlilty guy can't diagnose the problem, then I guess I'll have to go for the bucks and get a factory authorized tech to diagnose the problem. Thanks for your input.

  13. #26
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Mr. Apples,
    Am I missing something here? You have a contract with the utility company, I told you to call a real service company, not trying to debate over who's better,but since the utility company can't find the problem, you should hire someone who works on furnaces. So, you state you have a contract with them,and basically don't want to shell out the $$$ to a service company. Now, you're going to have your coil cleaned without even knowing if that's the cause of the problem(more than one thing can cause the limit to trip). and then,if that doesn't work, you'll think about hiring the service company. The smart money would go on hiring the service company now......
    If everything was always done "by the book"....the book would never change.

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