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Appropiate transformer for Boiler

lowwater Member Posts: 41

I have a Honeywell IQ thermostat hooked up to my Burnham Steam Boiler. However, the thermostat resets itself a few times a day. I am wondering if there is an issue with the transformer, or if I needed a bigger one. This is the transformer currently connected: Honeywell AT140D1012 Transformer, 40 VA (24V).

Would it makes sense and/or can I upgrade this?



  • Captain Who
    Captain Who Member Posts: 452
    Are you sure it is an issue with the transformer? When I installed a digital thermostat 7 or so years ago, I had to install an isolation relay so that the tstat was always getting power regardless of the state of any of the controls (which are basically on/off switches). Until I did that I had an issue like you describe.
  • John Mills_5
    John Mills_5 Member Posts: 946
    What's an IQ? Like a Vision Pro or Prestige IAQ?
  • Zman
    Zman Member Posts: 7,447
    I doubt you have a transformer problem. What model T-stat? Do you have a 3 wires or just 2 ? What else is on the transformer? Zone valves?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • lowwater
    lowwater Member Posts: 41
    John... Correct: Prestige IAQ

    Zman: Honeywell YTHX9421R5010 Prestige IAQ Thermostat Kit. 2 Wires. Not sure what else is on the transformer.

    Captain Who: that sounds interesting. Is that something I need to hire an electrician for?

    @all... I am not an expert, just a homeowner who is trying to learn a thing or 2... Appreciate all the answers so far!
  • unclejohn
    unclejohn Member Posts: 1,830
    You most likely need a common wire run to the "C" terminal on that tstat, unless it takes batteries.
  • lowwater
    lowwater Member Posts: 41
    edited December 2014
    There's actually an EIM box in between the thermostat and the transformer. However, I noticed that the blue wire wasn't spliced out of the transformer, but went to the control relay first, and was spliced out of the control relay back to the EIM (and thermostat). I've fixed this, so hopefully that will solve it!
  • icesailor
    icesailor Member Posts: 7,265
    MANY of these electronic thermostats require a Isolation Relay to resolve issues of multiple low voltage sources.

    I found that if there was a hint of a suggestion of using Isolation relays, it was best to use them.