It looks good on paper, also you own the boiler after 5 years, I would look into the maintenance contract that you will most probably have to take out and see if they do an annual subscription type of plan.
If you can afford to buy it outright you will reap more benefits, but like most of us it is a big layout, so quite a few sums to do to. I will be looking at this after it has run a while as mine will need changing in a few years.