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    Programmable thermostat went blank

    Asked Aug 29, 2006, 09:50 AM 14 Answers
    Our thermostat (which has been serving solely as a thermometer since the last time we used the heat in the spring) blanked out yesterday afternoon. I checked the inside temp. during the day, then last evening the face was completely blank. It is completely unresponsive to any button pushing. I checked for batteries, but it appears to be wired to the house electrical system. The tech at BatteriesPlus saw no battery in the diagram and digital photo I made. What might be the problem? It's only 3 years old. Thank you for any help you might offer.

    Last edited by janalan; Aug 29, 2006 at 05:44 PM.
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    rickdb1's Avatar
    rickdb1 Posts: 185, Reputation: 15
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    #2

    Aug 29, 2006, 04:49 PM
    First place to start is the batteries...
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    jgj6331's Avatar
    jgj6331 Posts: 153, Reputation: 19
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    #3

    Aug 29, 2006, 07:23 PM
    Most programmable thermostats have some form of battery - either replaceable or rechargeable - otherwise all the programmed information could be erased anytime there was even a momentary loss of household electrical power. 3 years would likely be the life limit of replaceable batteries. Do you still have the owner's manual? If not, try looking your t-stat up online. Many manufacturers have online manuals...
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    letmetellu's Avatar
    letmetellu Posts: 3,151, Reputation: 317
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    #4

    Aug 29, 2006, 09:15 PM
    How many wires are going to your thermostat?
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    janalan's Avatar
    janalan Posts: 4, Reputation: 1
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    #5

    Aug 30, 2006, 07:19 AM
    Only four of the ten wires coming out of the wall are connected to the thermostat. 3 are connected at one box at the Heat Stage terminal, the Fan terminal and the 24 VAC Hot terminal. The fourth wire is connected to a separate box at the 24 VAC Comm terminal. It is a Carrier Battery-free thermostat, I have learned.

    I spoke with someone at Carrier and he felt that there could be some problem with the system, not just the thermostat. I'm interested in any input, but will probably end up calling for service. I appreciate the help all have offered. Thanks!
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    jgj6331's Avatar
    jgj6331 Posts: 153, Reputation: 19
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    #6

    Aug 30, 2006, 07:58 AM
    Sorry we couldn't be of more help. A battery-free T-stat has a memory chip (PROM) that stores info that can be recalled - even after a power failure. But otherwise, it does need power to function. Start with simple first - make sure the breaker isn't tripped / fuse blown in your breaker / fuse box. Next, check the t-stat itself for a fuse. Lastly, you could test the 24 volt transformer using an AC volt meter across the 24 VAC comm and 24 VAC hot terminals.It should read around 24 volts.
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    janalan's Avatar
    janalan Posts: 4, Reputation: 1
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    #7

    Aug 30, 2006, 08:13 AM
    Thank you! I had checked for a tripped breaker already, but looking at the circuit board, I feel I'm entirely out of my league. All the responses are much appreciated and very helpful. I feel more confident now that I really DO need to have a service person come to the house and that makes the cost a bit easier to take! I will definitely use this service again. All of you who are volunteering your time and knowledge are to be commended! Sincere thanks.
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    jgj6331's Avatar
    jgj6331 Posts: 153, Reputation: 19
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    #8

    Aug 31, 2006, 06:22 AM
    Janalan,

    Please be sure and let us know the final outcome in as much detail as you can. It could possibly help someone in the future and will only add to the knowledge base on this site. Thanks...
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    janalan's Avatar
    janalan Posts: 4, Reputation: 1
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    #9

    Aug 31, 2006, 07:38 AM
    I phoned to request a service call yesterday afternoon and in talking with the scheduler, was reminded of an on/off switch that is mounted to the side of the furnace in the laundry room. It had gotten switched to off. Upon turning it back on, the thermostat began working just fine. I felt fortunate that the scheduler had just had a similar thing happen to her and that she was service-oriented enough to mention it to me. I feel a little silly, but I'm so grateful to have found this forum where problem-solving is offered so kindly.
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    agem59's Avatar
    agem59 Posts: 3, Reputation: 1
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    #10

    Apr 23, 2007, 06:10 AM
    I have never signed up for a forum, but HAD to share my excitement! I, too, did EXACTLY like the initiator of this discussion. Saw the house temp in the early part of the day, had a totally blank readout later in the day. I looked online for help, ended up here. Many thanks and much gratitude to the individual who asked him to post the outcome. THAT is exactly what my issue was. We have a switch indoors and another in the furnace room/utility room, where I store gardening equipment, etc. and this being spring and all... The switch was accidentally moved to the "off" position. One flick and I was back on track. I cannot thank you enough for having this information available to the homeowner!
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