servicing?

i have a vulcan continental 45/60 de lux i have used thermal couplings from b and q and local plumber supplies. this was in the house in 1976 and had been in for a few years prior to me.. the universal couplings last for around a year but the original lasted for years and years. my question is how often does it need to be serviced and what are the pitfalls. my one has been cutting out and assume the bank of flame holes is in need of a good clean and when doing so the asbestos rope seal will need replacing .i am not doing it it will be a heating engineer but they only seem to know about modern systems. any advice will be appreciated thankyou