Vaillant 282 water pump runs continuously?

Pump runs all the time when either hot water or/and central heating is switched on. During winter holidays I leave CH (HW off) on all the time and rads on frost but electric consumption is quite high for only the fridge also switched on. I would have thought pump should only operate when system demands heat. I seem to remember the pump never used to be on all the time.

Peter Renard
January 2010