What's wrong with my heating & hot water?

[TheCrowFromBelow]

It's not heating up. The boiler is firing up when the thermostat is turned off/on; the 3 way switch is moving as it should and I can feel water rushing through the pipes, but the water is cold! It is cold right next to the boiler, and in all the pipes around the airing cupboard.
I've tried bleeding all the rads except the one in the kitchen that I can't find where the key goes but to be fair, all the radiators were heating up fine yesterday. Can I do anything or do I need a professional?