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digital t-stat

ed med m Member Posts: 65
when i jump out the tsat, boiler fires and i have a reg. round mercury swith t sat in now and it is working but the digital will not and it is hooked up the right way and the little flame signal goes on on the bottom conrner of the display,but iam am still only getting 16 volts so not sure if t-stat is bad or not enough voltage to make the swith?
thanks for your help


  • ed med m Member Posts: 65

    had to switch out a t-stat went bad, replaced it with a new honeywell digital,would not work.tested the wires and only had 15 volts,very old cloth insulated wires. would the lack of voltage be a cause of t-stat not operating.steam boiler which they put a hw baseboard loop off for heat in basement.they rewired boiler in to a argo switching relay,and have powerd the up satirs t-stat of the same transformer in argo it possible that because the basement bb loop,with aquastat,tstat,as well as cirulator relay,and the up stairs t-stat for steam are off one transformer this is limiting power to upstairs t-stat. thanks for your help

  • Tom HopkinsTom Hopkins Member Posts: 539

    Jump the 2 wires together (R & W). If the boiler comes on, then most likely you dont have the wires connected to the right terminals on the thermostat. What model thermostat is it? Some need 2 separate wires for transformer and 2 separate for boiler circuit. Most nowadays just need the 2 for boiler circuit and have batteries and a jumper between R & RC. Hope this helps. -Paul Astoria Fuel [email protected]
  • Empire_2Empire_2 Member Posts: 2,343
    Bos, I agree...

    But is the wire an issue? Especially the old fabric covered stuff. Jump as you said then check your circuit loaded and also disconnect to see it you are actually getting the 22 to 26 VAC at the load.

    Mike T
  • carol_3carol_3 Member Posts: 397

    Go back to the transformer secondary and see what voltage you have there. The thermostat doesn't cause low voltage--it just tries to deal with whatever it gets from the transformer. If there is low voltage out of the transformer secondary, then check the primary. The secondary should be about 1/5 of the primary.
  • ed med m Member Posts: 65

    volts are good out of transformer 120/24
    just low volts on t stat wires
  • John Starcher_4John Starcher_4 Member Posts: 794
    I would take a hard look.... the stat wire, then. It sounds like you have a bad spot in the wire that acts as a resistor, causing the voltage drop. You probably will need to replace the entire wire lenght.
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