The TH0470 single channel programmer for controlling heating is designed to be as user friendly as possible it is a perfect partner for use with a combination boiler. Having 7day, 5/2day or 24hr and 3 on and off per day make this suitable for all applications wiether it be a replacement or on a new system. With is unique frost protection facility offering more security. The Immersion heater timer is specificly designed for use with immersion heater as they use a higher amp rating than standard controls.