No water from hot water taps; Vokera Option boiler?

I have a Vokera Option boiler and have had no problems with the heating and water, until yesterday. I had to add pressure as the low pressure light came on. I turned the valve and added pressure and the heating worked fine again. But now i have no water coming out of my hot water taps, the shower or going into the washing machine. Anybody have any ideas what might be going on?