If you're not getting the indicator light on the on /off switch & if there's no display / fault indicated on the facia, the main PCB has failed.
When you have it repaired, be advised, the new pcb is sealed & comes with a pack of "jumpers" not the wooly kind! These jumpers have to be placed on the pcb in specific places depending on the model of boiler.
Just make sure the new jumpers match the positions on the old pcb.
Baz (CORGI Eng)
May 2007