See my edit.
Also a clean system is only a partial part in a healthy boiler.
Best not kept secret really, you may get better advice as to how to ensure a good system operation. I'm guessing you fitted yourself?
A service does not just make sure the boiler continues to work, it makes sure that it continues to work in a safe manner. Can you afford not to do that? Would cost you just over a pound a week for this vital task.
OK I'm getting the impression you think I'm already Gas Safe Registered... as flattering as that is I'm afraid you're 100% wrong. You also seem to think I'm some pre-existing forum member. Once again I can assure you I am not. I am just a naughty DIY'er (you can guess the rest). As for the ACS stuff... pipedreams atm, will prob. never happen. The truth be told I was hoping that the professionals would let me into their little gang if I said I was trying for ACS, it's hard to get any help on this forum!
Now please do me a favour and accept that I am a layman, and in that regard I have no idea what you're talking about when you use the term 'Residual Head'. It's a grundfos pump, boiler is Baxi Main Eco Elite 30
also a pound a week for a service??? who you kidding... that's £52 annually?? no chance not even in Bradford