Worcester bosch cdi 42 combi keeps firing every 10 mins?

I have hot water and heating but the boiler is firing up every 10 mins or so. It sounds like a tap is turned on for 2 seconds ends with a fart like noise. Then the boiler runs for say 10 seconds. Nothing is calling for heat and its doing it all night long and keeping us awake. I have put it on eco setting by pressing the eco button in case it was the water pre-heat but thats made no difference. Can anyone help?