Wiring a controller

To view a flow chart of how the touchscreen controller functions, see Sequence of Operation.

For instructional notes on installing or replacing a V-10 touchscreen controller, see Installing a V-10 touchscreen controller.

The controller is compatible with most common thermostats including simple single contact (mercury switch) types as well as most power-stealing-type thermostats.

The standard connection for common thermostats that provides a simple contact closure for the boiler is shown in the Electrical Wiring diagram below.

Touchscreen controller - electrical wiring diagram

Touchscreen controller electrical wiring ladder diagram

Controller board layout

  • The Therm. 24Vac (TB2 terminal 5) provides 24 volts AC to all thermostats (up to four). This connects to the “R” terminal on the thermostat.
  • Each individual thermostat’s “W” terminal connects separately to one of the controller input terminals Therm. 1 (TB2-6), Therm. 2 (TB2-7), Therm. 3 (TB2-8) or Therm. 4 (TB2-9) depending on the load it is intended to control.
  • Power stealing thermostats take a small amount of current from the 24VAC to operate their internal electronics. To complete the 24VAC circuit required to operate power stealing thermostats the controller includes an internal 2740 ohm resistor from the thermostat input to ground.

    This internal resistor limits the power available to the thermostat and for some models additional power is required for proper operation. Thermostats that require this extra amount of power (for example the Honeywell T8775) will have a resistor available from the manufacturer capable of supplying the required power.

    Connect the power resistor from the thermostat’s input terminal to the Therm. GND (TB2-10) terminal.