Boiler comes on of its own accord?

I have a Potterton conventional boiler, Suprima HE,with an EP6002 controller. In the last two days the boiler has started to come on three oir four times during the day, outside the time settings, when the CH and HW lights are both off. It's normally on for about 10-20 seconds. It may be coincidence, but if I go and turn the room thermostat down, it goes off.


It also came on in the middle of the night.

Anyone know what causes this, and how I can rectify it?