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  1. #1

    Thermostat power

    In the year I've owned my house, I've had to replace the upstairs t-stat batteries about 4 times, and never the downstairs. This spoke to me that it was either something wrong with the actual control unit, or the HVAC power wire? Recently it gave me a "bat lo" message in the middle of the night, shutting off the A/C and waking me up. I shook it and it resumed normal operation.

    Is there a simple way to test if it's either the unit or wiring? Is it as simple as taking a voltmeter to the wire? What voltage should I be looking for? Sorry if this seems DIY, I just don't have a good understanding about how t-stats are powered and what I should be looking for.

    The t-stats for both downstairs and upstairs are Honeywell programmables, at least 12 yrs old.

  2. #2
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    999
    Quote Originally Posted by Johnnyma45 View Post
    In the year I've owned my house, I've had to replace the upstairs t-stat batteries about 4 times, and never the downstairs. This spoke to me that it was either something wrong with the actual control unit, or the HVAC power wire? Recently it gave me a "bat lo" message in the middle of the night, shutting off the A/C and waking me up. I shook it and it resumed normal operation.

    Is there a simple way to test if it's either the unit or wiring? Is it as simple as taking a voltmeter to the wire? What voltage should I be looking for? Sorry if this seems DIY, I just don't have a good understanding about how t-stats are powered and what I should be looking for.

    The t-stats for both downstairs and upstairs are Honeywell programmables, at least 12 yrs old.
    Yes, this is DIY and any replies regarding troubleshooting are against the rules. Sorry.
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  3. #3
    Join Date
    Jun 2009
    Location
    Upstate SC
    Posts
    1,439
    Are you using cheap batteries?

  4. #4
    No, Duracells AAs.

  5. #5
    Join Date
    Jun 2009
    Location
    Upstate SC
    Posts
    1,439
    Has your problem just recently started occuring? You mention the stats are 12 years old.

  6. #6
    I've only owned my house for a year, but the t-stats are from when it was built (2000). It's been happening on and off over this last year - it seems to drain the batteries in the upstairs unit and the bottom one has been fine. So I guess to rephrase my question, away from DIY is, how are thermostats powered? Is it primary battery with HVAC power backup or vice versa?

  7. #7
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,395
    Quote Originally Posted by Johnnyma45 View Post
    I've only owned my house for a year, but the t-stats are from when it was built (2000). It's been happening on and off over this last year - it seems to drain the batteries in the upstairs unit and the bottom one has been fine. So I guess to rephrase my question, away from DIY is, how are thermostats powered? Is it primary battery with HVAC power backup or vice versa?
    Depends on the model thermostat, and how it is wired. Some are battery powered only, some are either battery or hardwired, and some are system powered with or without battery backup.
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  8. #8
    Join Date
    Oct 2007
    Location
    Austin Texas
    Posts
    1,802
    It also could be as simple as the upstairs t-stat cycles many more times than the lower one.
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  9. #9
    Quote Originally Posted by John Culpepper View Post
    It also could be as simple as the upstairs t-stat cycles many more times than the lower one.
    ...did not consider that, but it makes sense. That would imply that it is battery powered primarily...I'll have to check the model number and do some research. Thanks all!

  10. #10
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,378
    Consider upgrading to a system powered digital thermostat. These aren't sold at the big box stores and require a common wire connection so you will need a pro to hook it up for you. IMHO all digital stats should be common wire powered, but unfortunately most builders are cheap and use the battery powered stats.

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