I have a traditional boiler - I generally just have it on a timer - couple of hours in the morining then on before kids and I come home form school and off at night. Last year when it was really cold I was finding that it was taking ages for the house to get warm when the kids and I got home so I started leaving it on and just turning it down a bit while we were out. Still switched it off at night though. It didn't seem to make much difference, if anything, the bill was slightly cheaper than the previous winters (our DD went down a few quid), but as I only did it for a few weeks, I couldn't really swear that that was the reason.