well if you wana pay over the odds then be it.
It's easy to say that, but for the layperson it's very very difficult finding an independent you can trust. Obviously only trustworthy people come on this board but there are a lot of sharks out there and whilst £230 sounds a lot it could still be a lot cheaper than the wrong independent and is guaranteed by the mfr, always a bonus.
My first experience of getting a boiler fixed cost me around £370 for an air pressure switch to be replaced on an apollo fanfare, from what I gather the switch itself was £80 quid so back then (10 years ago) I was charged £234+VAT for labour which included him going away TWICE to get the correct switch (the shop gave him the wrong one the first time he said).
I'm no heating engineer, but he found the fault in about 20 mins and it took not much longer to replace, so the rest was just made up/travel time and "going over the hour" several times.
My most recent previous boiler had the 5year WB extended guarantee which I paid for and apart from their guy breaking it on its first service I think that was a good deal from a co I would trust.
If I could cover my "new" boiler (a Gloworm Ultimate 80FF) with the mfr I would do so in an instant but it's just too old