I wish I'd asked how to set holiday set back mode, how to reduce the temperature of hot water, how to adjust the schedule to maximise solar pv and/or economy 7. 

I'm still not clear on the setting he has inputed with regards to flow temperatures. 

I wish I'd written down what he did say...

It is a requirement stipulated in Part-L of the Building Regs that you are provided with this information.

That installer's work isn't completed until you are able to operate, maintain and maximise the efficiency of what has been fitted.
As such, the invoice (or final payment thereof) shouldn't be settled.

And to answer the original question:

1: Here is the Report from the independent survey I had done to assess the energy requirements of my house. Provide a quotation to meet this, identifying the equipment and controls which you propose.

2: I wish to see photographs of other HP installations you have completed.

3: I wish to see site-specific schematics, annotated photographs of the layout and the guarantee terms you have provided on previous installations.

4: I require a control & monitoring system which reports the efficiency (COP). It needs to store a minimum of 12-months readings, and must be capable of being viewed remotely by anyone to whom I give the password.

5: I will be paying in installments, with the final 10% released one month after final commissioning. The final payment depends on the system meeting the efficiency level which you stated in your initial quotation.

2) Do you really know what you are doing?

3) By installing it there will it fulfil planning permission, building regulations and manufacturers requirements for space around the ASHP and boundaries?

4) Why are you installing a buffer, how will the buffer pump be controlled?

5) Do you have a design and full set of scematics to work to?

#### If you search my posts you will know why i have said these!! - and yes, my install still hasnt finished 3.5 years later ####

1. Ask them about the flow temperature they are designing to. A lower flow temperature (35C for example) will mean more radiator upgrades but will really help long term running costs. If they come in and say “yeah we run it at 55 C so you can keep all your radiators” then just be aware that what you save in initial outlay, you’ll pay for many times over in your bills.
2. Where you are changing radiators, try to get them to walk round with you and say what sizes are going where. For our install they initially wanted to swap a P+ for a K3 in the hall which looked fine on paper but made the hall too narrow in practice so they did a quick swap at the merchants on the day for a longer K2.
3. They should be advocating weather compensation controls and not on/off, fixed flow temperature type controls. After all the effort Hive, Tado and the like put into pushing you to micromanage your boiler schedule, you need the opposite approach with a heat pump running weather comp.
4. Ask about other projects they’ve done locally and see if you can speak to any customers about their experiences. (I notice NESTA have set up a ‘Visit a heat pump’ scheme which will also be useful once it gets going.)

An extra piece of advice, listen to some of the BetaTalk podcasts by Nathan Gambling- a very useful insight into the technology and the whole journey of having a heat pump installed. It really helped me to have that extra background when dealing with the installer.

I wish I'd asked how to set holiday set back mode, how to reduce the temperature of hot water, how to adjust the schedule to maximise solar pv and/or economy 7. 

I'm still not clear on the setting he has inputed with regards to flow temperatures. 

I wish I'd written down what he did say, and ask what sort of common failure modes he has experienced and directed solutions on them.