I have Potterton Kingfisher 2 RS60, 18 years old, it recently developed problem.
Occasionally pilot goes out when boiler is switched off for a night. It stays on after igniting, and thermocouple shines red, but when set for burner, it works for several seconds and it stops with pilot out. I need to repeat start up procedure dozen of times before boiler starts working again. This happens 3 or 4 times a months. So far I have changed thermocouple 3 times, pilot assembly.