Why would you be looking at a retailer's web site "as a possibility"?
Shirley you just need to choose a boiler, then get the installer to supply it to you.
If you procure the boiler yourself then you can wave goodbye to any interest from the installer come the day the boiler goes wrong.
If he goes into one of their 'shops' they will usually be able to give him about a dozen business cards for 'geezers' who will fit anything no questions asked for cash,allegedly.
That mob are still selling hundreds of SE boilers a week to 'white van man'.
