: Advanced Installation and Configuration Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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A boiler only system still needs a common. The best solution is to run a 3rd wire to the boiler and tie into the common. Many boilers will only have
T-T terminals and not have a common terminal.
In these cases, the common can be picked up directly from the transformer.
If it is not possible to run a wire, Fast-Stat makes a different accessory called a Common Maker that can be used. The ecobee PEK, Venstar
Add-a-Wire, or Fast-Stat Wiring Extender accessories mentioned above cannot be used.
The W call gets piggy-backed on the common wire with the small black sender module installed at the thermostat. Then the Common Maker is
installed at the boiler where it separates the W signal from the common.
Humidifier (1-wire)
A200463
When the accessory is NOT internally powered, it needs power from the furnace or fan coil. Connect one wire to the ACC+ terminal on the thermostat
and the other wire should be connected to Common. Because there is already a common wire from the stat to the air handler, and since the humidifier
is likely right next to the furnace, this is referred to as a 1-wire application because only one extra wire needs to run through the walls.
