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    don82's Avatar
    don82 Posts: 1, Reputation: 1
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    #1

    Apr 4, 2010, 03:53 PM
    Furnace sending 28V to thermostat, normal?
    The heater is at least a 7 year old natural gas furnace by Lennox (model G50UH-36B-090-05) and the old thermostat a Honeywell programmable thermostat (model RTH230B).

    So first off let me describe this and see if maybe these might be symptoms of something else. The thermostat started acting up near the beginning of winter by simply issuing a constant low battery within days of replacement with brand new alakine ones. This week however, it stopped initiating heating regardless of how cold it got (thankfully spring is here so only a couple chilly mornings). It also wouldn't initate cooling either when the thermostat was finally registering warm enough to require it. The Fan switch though worked fine, though it also turned on the AC regardless of the Heat-Off-Cool switch. Further, today while pulling it apart multiple times testing, it suddenly started showing the heating and cooling symbols. Given it's odd behavior I feel it's probably best to replace.

    Anyway after pulling off the old thermostat I saw that it was a 3 wire line coming in and from which they split the green line to fit on both the G and Y terminals of the thermostat (R was on Rh with a jumper and White was on W). I figure this is the culprit for why the AC and Fan are starting together as I found when I pulled the front panel off the heater to look at the circuit board that it's supposed to have a 5 wire line out (R,W,Y,G,C though the thermostat has no C input). I figure the installer (previous owner or who they hired) used the old thermostat line instead of replacing it. I decided though to replace this line with a 5 wire one, after replacing though I decided to test the voltage from the heater to make sure everything was coming in right. I found though that it was showing around 28V instead of what I thought was supposed to be 24V.

    Is 28V normal as I was seeing everywhere talk about 24V? If not could it explain the behavior of the old thermostat and is it a sign of a problem with the heater? Thanks for your time!
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Apr 4, 2010, 05:14 PM

    28 V is fine.
    Missouri Bound's Avatar
    Missouri Bound Posts: 1,532, Reputation: 94
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    #3

    Apr 5, 2010, 08:39 PM
    Does everything work now? Did you fix the problem?
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