Thanks for all the latest replies everyone! I was surprised to see so many pages!
I do take the point made about the engineer's overheads, but I think that these can only be so much before it becomes adding on extras for the sake of it.
I was worried that I had done the company an injustice with my guesswork on the prices, so I did look up the additional items, and as some of you have pointed out, my estimate for the extras was inaccurate.
However, I came up with a total of just over £1320 (not including VAT) for the parts, which included a Vaillant flue kit, the wireless thermostat set-up, the magnetic sludge filter, the Pegler valve and the fused switch. This, I acknowledge, doesn't include odds and ends like pipe fittings, length of wire, and rust inhibitor etc, so I will account for that below.
Working backwards from the original quote (not including VAT again), I came up with a total of £1088 for the fitting. So, let's take off the £88 for the odds and ends. Surely that's enough for bits and pieces isn't it? So, that leaves £1000 (not including VAT) for the actual labour charge.
We were told it was a one-day job, so if they take eight hours I make that £125 (+VAT) per hour, or if it takes them twelve hours then that's just over £83 (+VAT) per hour. Having read around online, I have found figures of £30 - £40 per hour as being considered a good price for this kind of work, and a lot of people were saying they work for a lot less. So, I don't think that I was too unfair in my estimate of a good pay rate for these people as being £40 per hour.
£200 for a day's work, as mentioned in this thread, is only £25 per hour, assuming an eight-hour day, so comparing that with my estimate above for the quoted job, an eight-hour day at their rate is FIVE TIMES the £25 per hour for a £200-a-day job.
Honestly, I am really pleased for anyone who can charge their customers £80 - £125 per hour and come away at the end of the day feeling that they have been adequately compensated for their expertise, and also given the customer value for money. But, having looked into this quote in a little more detail I just can't see how it is even getting close to a fair price.
If the other quotes that I am going to get come in at a similar price then that must be the going rate, and we may end up having to pay it, but I'm not happy with the idea of paying someone in excess of £80 per hour to change a boiler!