Central heating not starting but hot water okay?

I have a Worchester 14/19cbi boiler and yesterday the central heating stopped working although hot water is okay.

Here is was I have tried so far;

Resetting the electronic timers to manual
Turning up the thermostat and checking for click noise
Turning the power on and off

If I request a boost of hot water that works fine and the boiler ignites into life.

Any attempt to request central heating to kick in either manual or automatic on the thermostat does nothing?

Any help or guidance would be much appreciated?