Well, they came, they saw, and they went away again.
They're coming back next week to replace the immersion heater...but all under contract...no cost to me.
We had BG install the heating from scratch when we bought the house. They were a little more expensive than others, but not much. They did do a proper estimate. And a very proper job. We've had the maintenance contract ever since and had our money out of it too.
I haven't a bad word to say about them but, as the engineers who visited today said, it only takes one bad apple.....