baxi 401 back boiler pilot flame?

I have a problem igniting the pilot flame on the back boiler baxi 401. The boiler is old and I dont have a manual, so I am not sure how to reignite the pilot flame.
The boiler has performed ok since I moved into the house but occasionaly the pilot flame goes out and the boiler is a nightmare to start again. What is the correct procedure for startiing the Baxi 401 boiler, and where can I download a service manual