I spent 2 hours with Thermostat vendor, Ecobee and they couldn't help me. I have R,G,Y,B and the white lead is not connected. I need some guidance on how to get a Common wire. I tested voltage and R-G, R-B, R-Y all give me 26 volts. lead going to unit

So the red,blue,green and yellow were working fine with old thermostat, yet the Smart Ecobee3 needs a Common. This is the leads coming in.

Any suggestions on how to get the Common wire?

This is a Whalen unit, about 15 years old.

  • Can you give us a model number or a wiring diagram for your unit, or a closeup of the transformer (look top left in the first photo) for that matter? Commented Aug 5, 2017 at 3:09
  • I may have solved this in another site forum. Appreciate your assistance. I come back if I haven't solved it. Commented Aug 6, 2017 at 14:28

2 Answers 2


You need a "Power Extender Kit (PEK) from Ecobee. I am surprised that the PEK wasn't included in your purchase of the smart thermostat. Mine was.

Visit their web site at


Their web site also has a "Live Support" ; or, you can call them at 1.877.932.6233. They provide very good support service.



There are 4 wires coming from the transformer. Two are high voltage and two are 24 volts. It should be labeled on the transformer. Find the two 24 volt wires. One of those wires will trace back the the red thermostat wire. The other one is the common.

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