Vaillant combination boiler

[plumprobs]

I cannot get hot water when the switch is to hot water, but can get hot water when switch is set heating and hot water - what is the cause

 

[Beerlover]

I assume you are talking about a turbomax 242/1, black front with green knobs.

If so the microswitch on the diverter has failed, or possibly the valve itself.
Try a new switch first.

 

[Agile]

Before trying a new switch just watch to see if the lever is moving.

If not then move it manually and the boiler should fire up.

Tony