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    is this normal? : thermostat & furnace question

    Asked Jan 3, 2007, 02:02 AM 21 Answers
    Hi all...

    Firstly, I read a lot of posts before asking this question... I saw some similar questions but didn't find the answers I needed...

    It would be very helpful for me if the follwing could be answered (I'm a first time home owner, in the process of learning stuff, pardon my lack of knowledge):

    (PAYNE FAU -- 80% -- NG -- 6 years old -- start cycle looks fine)

    1. When I turn the heat on, (lets say HOLD at 68F) and the temp is at 59F, the furnace starts, then after it reaches about 61/62F it turns off, the thermostat says system off, it then kicks in after 2 minutes... Does this mean it is getting over heated?? I can increase the hold temp by 2F (in this case to 70F) or turn off & on and it would turn on immediately, which should not happen if its overheated right?
    Is this normal??


    2a. After it reaches the final temp 68F and it turns off, sometimes it turns back on in 1 min, is this normal??

    b. It also turns off and on every 10 minutes, is this normal? (note the temperature display in the tstat does not change)... Is the tstat TOO SENSITIVE, responding to changes under 1F??


    3. It takes 30 minutes to raise the temp from 57F to 60F (experimental) with 1 stop in the middle, the house is 1700sq ft, don't know if this is the normal rate at which these furnaces work... would bringing a HVAC person help make my furnace more effficient?


    From the other posts I gather that it might be dirty heat exchanger, faulty gas value or bad flame sensor... is that true?

    Answers to these would be very helpful... thanks for your time...

    -Anand

    Last edited by ramasund; Jan 3, 2007 at 02:19 AM.
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    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #2

    Jan 3, 2007, 07:47 PM
    Go to the furnace. Jumper the R and W contacts. If the furnace comes on and stays on as long as the jumper is in place, the trouble is in the thermostat or wiring. There is an adjustment in the thermostat that I have never touched, and usually suggest leaving alone. Dig some more here looking for instructions on setting the anticipator.

    If the furnace shuts off with the R and w jumpered, then look at the high limit switch.
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    ramasund's Avatar
    ramasund Posts: 18, Reputation: 1
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    #3

    Jan 4, 2007, 12:15 AM
    Thanks Labman for the reply!

    I will short the jumper and see if it runs continuously... Is is the same if I short them at the thermostat or the circuit borad? (should be, I'm assuming)

    I did an experiment today, running the furnace to heat the house from 57 to 67, the furance ran for 1 hour straight to raise the temp from 57 to 64 and then stopped for 2 minutes then continued for 20 more minutes to bring it to 67 (finally), so I think this 2 minutes break would be normal because of over heating rt?

    >>> I'm very concerned about the time it takes to heat the whole house... 80 minutes to raise the temp from 57 to 67??


    After heating to 67, it started cycling OFF-ON for 6mins-4mins for the first hour and slowly shifted to OFF-ON 10mins-3mins the second hour.

    >>> I think it might be the problem with the heat anticipator, but I can't find the adjustment to increase the resistance on it (its a honeywell thermostat)...



    I will do more experiments and update the thread... Thanks again...
    (I've scheduled a checkup with my heat company on 12th, hope they can figure out the issue)
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    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #4

    Jan 4, 2007, 07:43 PM
    Connecting the R and W at the thermostat does not eliminate problems with the wires, unlikely in this case.
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    ramasund's Avatar
    ramasund Posts: 18, Reputation: 1
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    #5

    Jan 5, 2007, 01:51 AM
    Thanks, I will do more experiments and update the thread...
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    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
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    #6

    Jan 5, 2007, 12:53 PM
    You need to look into the installers guide for the thermostat, many have settings for differential and heat anticipator. Set the differential to + or - 1 degree.
    Helpful (1)
    ramasund's Avatar
    ramasund Posts: 18, Reputation: 1
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    #7

    Jan 7, 2007, 02:08 AM
    Thanks!

    I wish I had the user manual... I can't even find the model number

    Anyway, when I set the thermostat to High efficieny furnace, it cycles 15-7 (off-on)
    And when I set it to gas furnace less than 90% efficient, it cycles 9-4 (off-on)

    I need to figure out how to set the differential (will look for the manual online if I figure out the model)... I'm almost sure I can't adjust the heat anticipator, because there is not one...

    Thanks again guys for the help!
    Helpful
    ramasund's Avatar
    ramasund Posts: 18, Reputation: 1
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    #8

    Jan 7, 2007, 11:44 AM
    Found it (the model number & troubleshooting guide)!!

    Here is the answer:
    --------------------
    The thermostat is calibrated to hold temperature within one degree of your set temperature to maintain an even room temperature. Because of this, the thermostat may seem to cycle more often than older thermostats that had a wider room temperature swing. Many people can feel a temperature change as low as two degrees. Since your Honeywell thermostat holds the temperature within one degree, the room air temperature remains steady and comfortable. The energy savings comes from setting the temperature back during the day when there is no one at home or at night when everyone is sleeping.
    Every heating system type will deliver heat to the house at a slightly different rate. The thermostat provides you with the flexibility to set the cycle rate adjustment to match your specific heating system, whether it is gas or oil warm air, high efficiency warm air, electric warm air, or baseboard hot water.

    A cycle rate is the ideal number of times a heating system will run, in an hour, to maintain temperature within one degree. For instance, a gas or oil furnace has a recommended cycle rate of 6. With a cycle rate of 6, the heating system, at a 50% load, will cycle 6 times per hour. This breaks down to about 5 minutes on and 5 minutes off. The actual on and off time of the heating system will vary as the load on the heating system varies.

    The installing contractor should have set the correct cycle rate on your thermostat. If you have questions on the cycle rate setting on your thermostat, honeywell suggests contacting a heating/cooling contractor.
    -----------------------









    Quote Originally Posted by ramasund
    Thanks!

    I wish I had the user manual... I can't even find the model number

    Anyway, when I set the thermostat to High efficieny furnace, it cycles 15-7 (off-on)
    and when I set it to gas furnace less than 90% efficient, it cycles 9-4 (off-on)

    I need to figure out how to set the differential (will look for the manual online if I figure out the model)... I'm almost sure I can't adjust the heat anticipator, coz there is not one...

    Thanks again guys for the help!!
    Helpful
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #9

    Jan 7, 2007, 01:08 PM
    Has the thing always worked that way, or at least since you bought the house? If you were sold a house with a messed up thermostat, you may be able to make the seller send somebody to fix it.

    Now that you have the model number, you might dig a little deeper yourself. Even if you don't have instructions, cycling through the settings could turn up the heat anticipator. Although I said such settings usually are better left alone, this may be a case for resetting it. Normally if a furnace once was running right, a problem is more likely to be a dirty flame detector or a sticky relay than the heat anticipator needing adjusted.
    Helpful (1)
    ramasund's Avatar
    ramasund Posts: 18, Reputation: 1
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    #10

    Jan 8, 2007, 01:18 AM
    It was probably cycling the same number of times an hour, except I didn't notice... It has been more than a year since I bought the house, so no luck there
    Helpful

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