The boiler seems to be working ok - there is heat in radiators, but no hot water. Also switch mechanism is dead for hot water, but lights up and can be adjusted for heating (and is part of the same switch) It may not be relevant but there was a power cut a few hours before this situation occurred.
I had exactly the same thing last week (without the power cut)
The gas board came out and it was the control panel with the switch mechanism on that was faulty - replaced and now working fine.