3/ I can’t fathom that at all. The heat pump will easily have a COP of greater than 1 when heating hot water and should be quite a lot more efficient than a immersion heater. 

4/ you can measure the conc of AF easily with a cheap diffractometer. I got mine off eBay for £20 I think. 

5/ I would guess you are right and it doesn’t fill me with confidence about the quality of the installation. 

Sorry to ask so many questions in one post but I'm still getting to grips with our setup.

We had an engineer out for a pricey service and they noted a few things. We have a Grant Aerona 17kw and a Grant cylinder.

1/ They have noted that 'LLH is not wired up'. I'm guessing this might be a mistake because the Low Loss Header (??) doesn't need wiring. It is plumbed in and as far as I can tell working.

2/ I think what he has meant is we have no DHW control wired for heating the cylinder from the heat pump. For some reason, we only have control over heating via a Hive thermostat. Last winter it became a problem because it was always prioritising hot water and struggling to heat the tank meaning it wasn't heating for long periods. Simple question - should I be controlling when the pump is heating the hot water? If so, with what? It doesn't need to be WiFi connected just a timer by the cylinder would be fine. The installer has always been adamant I don't need this.

3/ I noticed in the Grant manual that there was some suggestion you might turn your heat pump off entirely in the summer and use the immersion heater to heat the tank. Does anyone do this, and is this more efficient? Why would you want to do this? It is a 3kw immersion heater. 

4/ It has been noted that the Glycol levels are at -4c. It is Grant supplied Glycol and I'm not sure whether this is a limitation of the Glycol itself, or that it needs to be topped up to 7 degrees by concentration. I've been told I need to get the installer out to do this so I wanted to make sure I know what I'm talking about because they fob me off every time they visit. Is there a way to work out the concentration?

5/ I think it is minor but the pump to my underfloor heating goes on when the heat pump is heating the cylinder. It is only the pump, not the relays at the tank itself. I'm guessing the pump is wired to the wrong terminal. I'm guessing it will shorten the life of the pump, but how much does it matter?

With both the cylinder and the UFH would any electrician be willing and able to do the wiring? If I provide them with the diagrams?

Thanks so much if anyone takes the time to answer this long list. I'm so pleased to have this forum I've learnt so much and I really appreciate community. Hopefully, I can repay once I've gotten to grips with things.

Cheers.