"In all honesty I didn’t think about payback, at the time of ordering interest rates were rock bottom and I couldn’t think of a better annual return on £17k."
Forgive my slowness but I don't understand this bit. This isn't 17k you've invested.. isn't it 17k you've spent. So it takes ten years to recoup the expenditure and then you get a return? So 17k invested at ,say, 4% for ten years is, say, 25k. So at 2k a year "return" you've another 3 years to wait to break even? So at least 13 years?
