And they all have a vested interest.
Try and separate the mantras from what happens in the world outside. What, for example, does this "service" actually consist of? When I hear "is there a problem, the last guy was only here 20 minutes" and, "no ones ever checked the filter before", and "what's all the banging for?" it tells me that somebody has been charging for an ineffectual visit. They might have returned each year to tinker, drink tea and present invoice, but they have done little when they were there.
You also mentioned that an oil boiler can get sooted up if not serviced every year, while this is true in some cases, oil boilers can get sooted up even if they are serviced every year. Servicing will not guarantee a soot free boiler in the event of a fault.
Try and separate the mantras from what happens in the world outside. What, for example, does this "service" actually consist of? When I hear "is there a problem, the last guy was only here 20 minutes" and, "no ones ever checked the filter before", and "what's all the banging for?" it tells me that somebody has been charging for an ineffectual visit. They might have returned each year to tinker, drink tea and present invoice, but they have done little when they were there.
You also mentioned that an oil boiler can get sooted up if not serviced every year, while this is true in some cases, oil boilers can get sooted up even if they are serviced every year. Servicing will not guarantee a soot free boiler in the event of a fault.