The radiators can be turned up and down, and the boiler also has a heat setting.
I've tried having it on for e.g. an hour early morning, late morning, early afternoon, late afternoon and a couple of hours in the evening, but it gets really cold inbetween times! Also, it's on permanently for those hours, regardless of how warm the house is.
I just can't work out what's the most efficient way to use it!