Also what is the benefit of so many photos? Will they design a system before the survey?

I chose boxt after speaking to them at length and asking lots of questions related to the installation which I gained from this forum. They were very accommodating and gave me lots of time. Their reviews of heat pumps installs are very good on Trust Pilot are very good and @adrian here had a good experience with them too.

They are also installing one of the best heat pumps on the market. A comparative quote for similar install from one of my above options was coming to £9499 with my own radiator installs for 45c. Boxt are charging me £6299. 

Octopus were looking at June install which I didn't want to wait that long. Cosy 9 doesn't have enough reviews for me to say confidently that will be a good one for me with limited access to features.

I hope to keep everyone updated with details as I go along.

Our boiler man dried the circuit board with a hairdryer and it is working again.

Very sensible.

A damaged circuit board isn't a safety issue anyway.

This is precisely the sort of item which should be recovered from any boiler which is being decomissioned.
Wise heating-installers may hang onto them.

You're also likely to find 2nd-hand logic boards being offered on Ebay.
Enter your boiler model number and see what comes up.

As to the radiators, it is never too early to swap the old smaller ones out - if you are changing them all, you may even be able to reduce the flow temperature on your gas boiler a little and relieve the load on the poor old thing! Regards, Toodles

I am now chasing @adrian for more information about boxt install using the same Vaillant HP which includes all radiator upgrades for free. Their quote is higher by about 1k more than HG trained installers who are charging me 4k for 45c radiator upgrades (about 7 radiators) or asking me to get my own radiator install done which I know will be more than 2k if I ask my own heating engineer to do it as they charge VAT on top.

As Boxt are charging upfront there is no going back by the sounds of it so need as much info as possible.

dT should stay consistent but min (crucially max) flow temperature should be dropped as low as possible to maximise efficiency of you system. dT is determined by things like pump speed and system setup.

There are many, many factors that affect how well a heat pump system performs, most of these come down to either mechanical setup or controls/settings. 

If you can nail these, any well-reputed heat pump system will run well. Some manufacturers are regarded as better than others but it is definitely a horses for courses situation. 

There is some very solid advice here, as always. 

Re Heat Geeks, it is one metric of assessing an installer/designer's credentials when it comes to heat pumps but the most important factor is previous recommendations, reviews online and their ability to answer your questions in a way appropriate and understandable to you. I say this as a Heat Geek myself and know fantastic designers/installers who have never touched a HG qualification and some who are under HG and not so competent. It's one measure but not the be all and end all and it's not something I generally feel impacts my clients' decision-making (although I will always answer honestly if they ask!). 

You should feel comfortable with the installer, their treatment and knowledge of their craft and you should never be pressure sold anything. If in doubt take a moment take some time to step back and review all your options and seek advice. 

You should be provided with running cost estimates (and these are estimates only) under MCS and an explanation of your heat loss and how this figure was arrived at. If the installer is using a 3rd party company to design, they may allow you to contact them and discuss the design work but this does depend on the installer. I spent a lot of time in my previous role working with homeowners when the plumber was happy to allow me to answer all the techy questions and design aspects. 

Please let us know if you have any further questions. 

BW