How can I fix my Potterton Profile Prima boiler? Pilot light won't ignite?

I have had an intermittant problem with the pilot light on my Potterton Profile Prima boiler. Something (unknown) causes it to trip out from time to time. Using the small trip switch on the underside I have been able to reignite the pilot - UNTIL NOW. This time, the switch seems to be depressed in, and no amount of pressing/holding it will reignite the pilot. The pump is working and is making the usual sounds, but the pilot won't light. I did notice that the boiler shell was very hot to the touch although the hot water and CH were not working. Any suggestions would be very helpful. Thank you