Lockout?

I have a Worcester Bosch heatslave 20/25, 7 years old, serviced every year.
Boiler has stopped working, no hot water/heating, lockout light on, tried reset button, fires up for 30 secs, and cuts out, (full tank of oil ) Called out my service guy who tried new photocell and new control box, no joy, wasted money, Boiler still not working, tried booking an appointment with WB but they are not accepting ANY 'cash customers' assume they mean contract customers only, get their attention.
Any advice would be most gratefully received. Desperate !!!