vokera excell 80 sp no hot water unless heating is turned on?

basically I cant have the heating timer in the off positon (or in the timer controlled postion but off) and have hot water to the taps.
The heating has to be on to get hot water to the taps, and also the heating temp dial is controling thie tap water temp and the tap water temp dial is now contolling nothing.
any ideas anyone.
thanks in advance.
ken