Gentlemen!
Thanks again for the replies, the survey was just last week, and no makes or models were mentioned, so I reckon I will have a look at the ones available.
As the engineer was from the fitting company, [Warmfront having done the initial one which accepted me onto the scheme I think], and came across as very knowledgeable and professional, I think I should just go along with any advice that seems sound. I'll wait to see when they contact me and talk it through then.
Having spent a working lifetime as a Service Engineer and Manager, I do realise that not all personnel are on the same level, and that if a guy can't really understand the product, he'll tend to knock it if he can't fix it!
I'm extremely appreciative and genuinely surprised by the response from all of the serious respondents on this forum from so many parts of the country, taking time and trouble to write and share their experience, so many thanks once again.
Ian Colley, in sunny Stockport.