How can I fix my Vokera Compact 24 combi boiler?

Hello there.

I'm a complete novice when it comes to boilers and mine is really playing up.

It's a vokera compact 24 combi boiler and I have no hot running water, but the radiators are heating up fine? Regardless of whether I have the boiler set to water+radiators or just water, the hot taps throughout the house run completely cold. This only started happening yesterday and I'm really stressing that it's going to cost a packet to get fixed.

The pressure is fine and doesn't seem to have changed (which is pretty much the only thing I can check as if I opened the boiler up I wouldn't know what to look for).

Could someone please tell me if they think it could be something simple I could fix myself, as it's near christmas I could do without the expense of a plumber but I need hot water :(

Any help would be much appreciated.

Regards,