The Greenstar Comfort I (7733600001) is an intelligent programmer that plugs into the boiler & is supplied with a separate room thermostat. The thermostat has a load compensation function which enables the control & the boiler to have an intelligent conversation delivering a 3% Er P package efficiency increase when fitted with a gas boiler. This control simply plugs into the boiler & comes pre-paired with the room thermostat for a quick installation.