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Power Stat w/o Batteries (PICS INCLUDED)

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smithfan
smithfan Member Posts: 91
I'm trying to power my Honeywell programmable (rhh2300/rth221) stat without batteries and it's not working. I ran new wire from the Taco relay to the stat and wired the blue common to the 24vac on the board and then Red/White to the zone 1 switch. Screen did not turn on but my meter says I've got about 29 volts sitting on blue. Did I wire this wrong or are these stats only able to be operated via battery?




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  • Steamhead
    Steamhead Member Posts: 16,889
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    There is no "C" terminal on that thermostat, therefore it can only operate on batteries.
    All Steamed Up, Inc.
    Towson, MD, USA
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  • ratio
    ratio Member Posts: 3,649
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    The "B" terminal is used for certain heat pumps. As Steamhead noted, that stat does not have a common terminal. Were it present, it would occupy the terminal marked "not used", & be labeled "C".
  • smithfan
    smithfan Member Posts: 91
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    Steamhead said:

    There is no "C" terminal on that thermostat, therefore it can only operate on batteries.

    If I get a stat with a "C" terminal is the rest my wiring correct on the taco relay?
  • ratio
    ratio Member Posts: 3,649
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    Take your meter and go from the "R" terminal in the zone relay (where the red wire is landed now) to the two 24V terminals. One should show roughly 0 volts, that's the hot, the other will show roughly 24 volts (the 29 volts you mentioned above), that's the common or "C" terminal. Just to double check.
  • smithfan
    smithfan Member Posts: 91
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    ratio said:

    Take your meter and go from the "R" terminal in the zone relay (where the red wire is landed now) to the two 24V terminals. One should show roughly 0 volts, that's the hot, the other will show roughly 24 volts (the 29 volts you mentioned above), that's the common or "C" terminal. Just to double check.

    I got 0 volts on the top 24v input and about 1.25v on the bottom 24v. That's checking DC voltage from "R" terminal to both 24VAC inputs. Does that sound right? The 24 volts from the "R" cancel out both 24 volts on the common?
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    smithfan said:

    ratio said:

    Take your meter and go from the "R" terminal in the zone relay (where the red wire is landed now) to the two 24V terminals. One should show roughly 0 volts, that's the hot, the other will show roughly 24 volts (the 29 volts you mentioned above), that's the common or "C" terminal. Just to double check.

    I got 0 volts on the top 24v input and about 1.25v on the bottom 24v. That's checking DC voltage from "R" terminal to both 24VAC inputs. Does that sound right? The 24 volts from the "R" cancel out both 24 volts on the common?
    Uh... if you're still working with the transformer and zone switch, you should be reading AC, not DC...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • smithfan
    smithfan Member Posts: 91
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    smithfan said:

    ratio said:

    Take your meter and go from the "R" terminal in the zone relay (where the red wire is landed now) to the two 24V terminals. One should show roughly 0 volts, that's the hot, the other will show roughly 24 volts (the 29 volts you mentioned above), that's the common or "C" terminal. Just to double check.

    I got 0 volts on the top 24v input and about 1.25v on the bottom 24v. That's checking DC voltage from "R" terminal to both 24VAC inputs. Does that sound right? The 24 volts from the "R" cancel out both 24 volts on the common?
    Uh... if you're still working with the transformer and zone switch, you should be reading AC, not DC...
    Sorry, meant AC..I'm getting 0 volts from R to 24VAC and 1.8 volts from R to COMM..
  • smithfan
    smithfan Member Posts: 91
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    So now I checked W to the top 24VAC input and get 24volts. I get 0 volts on both 24VAC terminals testing from R.
  • smithfan
    smithfan Member Posts: 91
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    I figured it out, just had to probe it every which way. Bottom is common, got 29 volts on R. Top is 24 Volts hot. Now I just need a decent thermostat. Any recommendations? Wifi not necessary, but tired of changing batteries.
  • ratio
    ratio Member Posts: 3,649
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    Honeywell 5000 series for non programmable, 6000 series for cheap (relatively speaking) programmable. The 8000 series is last years' flagship, I like them a lot, but they're somewhere north of $150. I don't have any experience with their newest line, the T series.

    Avoid the big box store models-they seem to be second-sourced. I'd try to get one from a local HVAC supply house, but be aware that some places deal ...poorly... with homeowners. If they are less than helpful, spend your money somewhere else!

    smithfan