I bought two Ecobee Smart Thermostat Premium to replace our older Honeywell thermostats.

I checked both thermostats and their wiring matches and they do not have a C wire present. So I figured I’ll need to install the PEK to the HVAC control panel… …except, I go to the control panel inside and find that the control panel does have a C wire present.

I’m a bit confused since I don’t grasp why the control panel would have it when neither thermostats has it? Is there another panel somewhere I should be looking for like a zone panel?

  • CRM-3-VB-HD@alien.topBEnglish
    1·
    10 months ago

    C wire is the common. Just because it wasn’t attached to the existing T-stat doesn’t mean it’s not there. Pull the wire out from the wall behind the T-stat and see if they cut the C wire off short. If there’s enough slack, you may be able to use it.

    Btw, ecobee tech support is very helpful.

    • Lanky-Beginning-7555@alien.topOPBEnglish
      1·
      10 months ago

      You were right - the previous installer had wrapped the c wire around the others further into the wall on both thermostats.

      I did end up making a frustrating mistake following the directions - at first, since I didn’t find the C wire, I figured I would need the PEK and started following those steps. Ecobee’s steps for the PEK install said that if you have a zoned system [I do] then you’ll have to install it at the zone control and not in the HVAC control board.

      I did that and it blew a very hard to find fuse on the zone board - I ended up having to order online after not finding it at the various supply stores locally. When I called ecobee they said that the PEK should never be installed in the zone board itself - which is the opposite of what the app told me to do.

      Anyway, once I found the C wire I realized I didn’t need the PEK after all. I replaced the fuse after a few chilly nights and both zones are up and running now.