Thanks Karlo. had found that much out and had a look through some online manuals already but not found what I needed,
after all this system is around 30 years old! Waiting for Alde to get back to me.
Piggysteve,
If I sent a couple of photos of the boiler and the control panel you could maybe tell me if it looks anything like your system, although I don't suppose many of this age have survived!
Have considered that it may need a new thermocouple but would like to understand how it should work before trying to get parts replaced...it may just be down to human error rather than a faulty part :? :)