Fair play, its a toughy to say cos you have manufacturers destructions to follow or the general practice way in absence.
I always think its hard to justify a general service on a combi, think that might be why certain big companies call it annual safety check now.
i like doing a service on a bbf cos they need a clean and dismantling and checked where as combi, they generally get opened up to check inside, check seals in/on combustion internal, burner pressure, fsd check, check burner, h/ex etc. its more safety than replacing parts.
what makes you feel your mate was robbed????
iain
May 2008