Need help with Boulter Oil Boiler & Timer?

Have Boulter Camray 5 Boiler and the internal timer is faulty & has damaged PCP board. Had an external dual control timer fitted but we can't get it to time the hot water to come on & off. Have been told it is not possible to get an external timer to do this.

Is this correct?
Does anyone know where we can get an internal timer or a way of timing water with external timer. Our bedroom is above garage & when boiler fires overnoght for heat store it wakes us up.