Soldato
However it isn't cut and dry, since not everyone will require the same amount of work doing. So you can't just state £15k vs £2k and hope people will ignore it, unless you want to work for a newspaper making headlines that sound great but aren't true all of the time.
I've had quote from as low as £8.7k all the way to £18k for an air source heat pump, it is the last piece of my puzzle to get rid of gas for good, this is for the same house with the same requirements, just different vendors/installers. Obviously that is more than a boiler, but I needed a new water tank anyhow since the one I have is from the 60's/70's and with the inclusion of Solar I can now use that to also heat my water, I am also redecorating several rooms, all of which are having new rads, since most are totally shot. So as you can see just swapping out my 20+ year old boiler would be a bit cheaper, - my individual circumstances - everyone's will be different and just splatting £15k vs £2k is a lie.
Interesting you post this because you've almost validated my point.
Your estimates range pretty wildly, neither the £9k system and the £18k system may be fit for purpose...
As the poster I was responding to said, a badly designed system is going to be inefficient and expensive. My point was; when you're spending potentially £15k on a heat pump system, you want to be sure it's right for your situation. A typical boiler installation, whilst can be expensive, is a lot less money for far fewer problems (ignoring the carbon footprint elephant in the room).