BOXT sounded good. A Baxi, Worcester-Bosch, or Vokera for around £2500 installed. They even tried to suggest a combi even though I'm on a shared supply, but I declined. There is obviously no need for a site visit to test water pressure or discuss my needs - that is just an excuse to try to get free biscuits, isn't it?
Then I looked at one of the suggested boilers. Despite being heat only, it only supplies 10.2 litres of hot water per minute, as well as having a N/A hot water flow rate. It also comes with a low energy pump, a free system cleanse (whatever that means), and a free filter worth £130. Must be a really good filter. And they can do it in a day.
I wonder if they know the Artex on my wall where the boiler is mounted has asbestos in it, or that they'd need to replace the entire gas run from the front of the house and can't lift the floor due to UFH?
No problem for them - the Terms and Conditions simply allow them to up the stated price when they get here and find that the job isn't so straightforward as it looked!