how to rewire from scratch my central heating system?

we have a baxi bermuda back boiler central heating system that is twenty years old now. we have replaced the pump, and now want to replace the programmer, cylinder thermostat, three port valve and room thermostat with a horstmann package to replace the ageing honeywell system. i need an easy to follow wiring diagram so that i can start from scratch. also can anybody tell me why my boiler and pump start up even when the programmer is off?