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Honeywell electronic tstat not working with new gas-fired boiler

I got a new steam boiler installed, and in the process converted from oil to natural gas. When we tried to call for heat with the existing Honeywell round digital tstat, the display shut off like it suddenly lost power. It seemed like the boiler controls (vent damper, gas control valve, ???) were robbing power from it. Is this a known issue?

My contractor replaced the tstat with a Robert Shaw RS3210. It runs on batteries, so it did not have the power robbing issue. Is this the tstat to use for steam?


  • lchmb
    lchmb Member Posts: 2,997

    I believe (depending on the model) that there is a resistor that should be installed at the boiler...
  • JStar
    JStar Member Posts: 2,752

    You can't use those Tstats on boilers with vent dampers because the damper will open the control circuit for a split second, shutting down the thermostat (loss of display), then recycle continuously. You can look for that resistor. I would rather not deal with the extra needed part. Especially since it could short out and destroy the boiler transformer.
  • lchmb
    lchmb Member Posts: 2,997

    I do agree with JStar on that. Better off to be done with it. Just change your batteries when you do your smoke alarms..:)
  • MEK
    MEK Member Posts: 15
    RS3210 runs off of 24 volt power

    I looked up the specs on this model. It is supposed to run off of the 24V from the boiler control, with the batteries as back up. So will this t-stat experience the same loss of power as my old one when the vent damper is operating, except it has battery power to fall back on allowing it to ride through?

    Does anybody know if I can set CPH on this tstat?
  • ed wallace
    ed wallace Member Posts: 1,613
    honeywell tstat

    why not install a taco control that will supply 24 volts to tstat at all times then just run low voltage to the boiler
  • JStar
    JStar Member Posts: 2,752

    Any non "power stealing" thermostat will work.
  • John Mills_5
    John Mills_5 Member Posts: 935
    Need a common

    If you want a thermostat to work off the boiler, it would need a common wire back to the boiler. So R, W and C. Otherwise, newer stats like you now have run off the batteries and shouldn't have any problems with your system. As they are all saying, your previous stat is "power stealing" and that's what is causing your problem. 
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