Go into the loft and give the float valve some exercise. Chances are that
it has stuck in the shut position and the water has evaporated away.

Hopefully this is the problem then you come down and bleed the air out of
the radiators and hopefully all should be well when you turn on.
Later bleed the air out again when the hating is off.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

I have checked the float valve and it seems fine the tank is full of
water. I have tried bleeding all the radiators but the upstairs ones
do not seem to have any water in them.