The ST620VBC comprises of the S series programmable room thermostat with an integral plugin RF boiler control. The RF boiler control is a direct replacement for the basic time clock or blanking plate usually supplied with the boiler. Installing the RF boiler control takes minutes. Once installed, you will benefit from all the control features of the Salus ST620 programmable room thermostat. A programmable room thermostat is a device that combines the functions of both a room thermostat and time controller into a single unit. The programmable thermostat is used to switch your heating system on and off as required. It works by controlling the temperature according to a series of programmed time settings that take effect at different times of the day. The ST620 programmable room thermostat is a stylish and accurate 5/2 or 7 day programmable electronic thermostat with a large, easy to read display. This programmable thermostat has been specifically designed to be used with the integral RF boiler control.