No water from hot taps with Vaillant ecoTEC plus 831?

System was installed 3 years ago and has worked well. Last few days we have been running in 24/7 and have lowered thermostat at night to background temperature and raised it again in the morning.

This morning I opened the kitchen hot tap and there was no water!! Opened bathroom hot tap and again no water. House nice and warm and central heating operating normally but I cannot get a drop of water from either hot tap.

Programmer looks normal and no error codes on boiler display (no 'tap' symbol either!). Last few days both were working perfectly and nothing has been touched or reset but suddenly, today, we have no water from the hot taps.

I've looked through the manuals and cannot find anything that mentions no water coming out the taps.

Anyone have any advice?

Many thanks

Baz