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New Wifi Thermostat with C Wire Transformer and Taco Zone Controller

I just added a new Sensi Wifi thermostat to my heat only system. With no C wire and no easy path to the basement, I added a plug-in transformer as suggested on the Sensi website (https://sensicomfort.com/support/article/adding-a-24-vac-external-transformer?product=wi-fi-thermostat). It all appears to be working BUT my zone light is lighted a pale yellow down in the basement on the Taco Zone Valve Controller. None of the other systems that aren't calling for heat have that light active. The pump isn't operating so no heat is flowing (good thing as it's 72F outside). Not sure what to make of this. Turning up the setting (either on the faceplate, using my phone or telling it to verbally increase with Alexa) will bring on the pump and open the zone valve (as well as light up the red light on the zone).

Any suggestions?


  • Jamie Hall
    Jamie Hall Member Posts: 18,738
    I'm not particularly keen on that arrangement, but... try switching the two wires from the wall wart transformer and see if that makes a difference. The yellow light indicates stray current from somewhere... you did clip the jumper as the instructions said?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • KevinWyman
    KevinWyman Member Posts: 27
    I did clip the wire. I think the stray voltage may be coming from the thermostat itself and its battery back-up. With the transformer unplugged, the yellow light persists. Still waiting to hear back from Sensi support.
  • KevinWyman
    KevinWyman Member Posts: 27
    So just off the phone with Sensi. Sensi Support tried initially to send me to Taco but then after several on-hold consultations they suggested cutting the other two jumpers PS-W and PS-Y. Still a faint bit of yellow light from the Taco Zone Valve controller. With the faceplace completely off, no light on the Zone Valve controller. Either with or without the transformer plugged in. (So I think that rules out the wiring in the wall somehow picking up stray voltage from a nick etc.).Offered no other support or explanations.

    I received my second Sensi Wifi tstat today and plugged it into the base and the light returns very brightly. I only cut the red jumper.

    Should I just ignore the light?