If your current thermostat is controlling a boiler and only has two wires present:
- Check to see if there are any spare wires behind the thermostat that you can potentially use
- Verify the terminals at your boiler that the thermostat wires are connected to
Most boilers usually have T & T connections. T & T connections require a dry-contact to open/close the control circuit to engage the boiler. Boiler controls typically require only an open and closed contact switch, therefore a relay is used to separate the 24VAC that is returned as a control signal from the ecobee.
If you have T & T connections, the ecobee will not be compatible right out of the box, but there are a few steps you can take to make the ecobee compatible with your setup.
Use an external 24VAC transformer (requires 4 wires)
An external transformer will ensure a consistent 24VAC to the ecobee, allowing the thermostat to power on. If you are unable to run additional wires from your thermostat to your boiler, a plugin transformer near the thermostat is the simplest solution. If you can run at least two additional wires from your thermostat to your boiler (or if you have some spare wires), you can install the transformer at the boiler level. The picture below illustrates how this setup works.
Use an external 24VAC transformer with a Fast-Stat Common Maker
The Fast-Stat Common Maker (purchased separately) will create a C wire with the wires you currently have by splicing those wires together with the wires from the Fast-Stat. The external transformer will provide power to the ecobee and give the Fast-Stat a common to tap into. The picture below illustrates how this setup works.
Use an external 24VAC transformer with an isolation relay
If you have at least three wires to work with, you’ll want to install an external 24VAC transformer as well as an isolation relay.
We recommend a single pole normally open (SPNO) 24V isolation relay.
The picture below illustrates how this setup works.
NOTE: The W1 and C wires should go into the terminals marked “1” and “3” on the relay.
For more information about how to install the ecobee with two-wire heat-only systems, please refer to the following link: