Worcester Bosch Greenstar 24i not firing up?

I have a worcester bosch greenstar24i boiler (6 months old) which is not firing up. We have hot water but the heating won't come on. It seems that the Digital thermostat transmitter is talking to the boiler as when you increase the temperature you can hear a click but then nothing happens. I have changed the batteries in the programmer and re-done the binding process but to no avail! Can anyone help?