if you dont use vaillants controls the hot water dial is inactive...
By Vaillant controls Alec means your programmer thermostat wiring centre etc
If you use their controls then the dials do as u are expecting
If third party controls are used the boiler is only told to fire not if it is for heating or hot water and is then diverted to whichever the controls are telling it.
I prefer to use vaillants own controls but this doesn't mean yours is wrong
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