Fit a room thermostat to control the central heating circulation pump. If you use a digital thermostat you can control times as well as temperature. eg:-
6:00am to 8:00 am 22 degrees.... 8:00am to 4:30pm 15degrees... 4:30pm to 11:00pm 24 degrees... 11:00pm to 6:00am 15degrees
Pete, January 2007