Worcester Heatslave 15/19 not working?

Hi,
I have a worcester heatslave 15/19 combi boiler which worked fine until this morning when it suddenly stopped working halfway through a shower :( The power light and the lights which signify the water and heating are on all work ok - the lock out light and the reset light are not on. The boiler usually makes a couple of clicks and then fires up, but it's not firing at all - have checked and there is plenty of oil - any ideas? The plumber can't come out for another day and even he was a bit unsure as to what could be causing it so any ideas would be much apperciated.