new valve and pump fitted heating fine no hot water?

Just had an engineer to fit a new c/h pump and 3 way honeywell v4073a motorised mid position valve to a combi boiler system where the upstairs boiler is heated to provide hot water,problem is put heating and hw on together and the heating is fine but the water remains cold,as does the tank.
by messing with the controller I can get get hot water but not both ch and hw together.
Engineers been back but cant sort it!!!
any ideas plz could it be the controller? but didnt have this problem before the work was done