Why does my Vaillant ecotec boiler keep kicking in through the night?

Your boiler will have the warmstart function enabled, this is to pre-heat the hot water.
If you look at the display there will be a 'C' on there, indicating it is on.

Turning it off is simple, turn the hot water (top left) dial all the way down to minimum, the C will disappear from the display, now turn the HW dial back up to your desired position.
Do not turn it all the way up again, as the C will re-appear, and you will have re-activated the warmstart.

Carefree
January 2011