When the boiler is on the light is on and when hot water is run it fires up fine. However, when we put it onto constant nothing happens and we currently have no heating. Any tips would be gratefully received.

Sam Withell, January 2007

The problem lays with either the time clock or the pcb.
If the time clock is digital, try resetting it. If it is mechanical then it will not be the cause.
I have had occasions with this model where the pcb (printed circuit board) has not responded to the command from the time clock.

David Hickey, January 2007