There are always going to be difference of opinion on what boiler to go for, but in my experience I would be suggesting to you the Worcester 25si or the 30si. Good reliable boilers, never have any problems (when installed correctly) and with excellent backup service from Worcester. 5 yr warranty not a problem. But check out the write ups on different models and ask friends and work colleagues. Recommendations always help.
His chosen boiler has probably had it's first annual service by now!
I knew that but I could say in my defence that I posted the comment for others that may have similar probs. Thanks for the comment though, it made me smile.