@alleyfish - excellent list, I would add, only it takes the list to eight and so loses the alliteration of seven deadly sins, "Of course your heat pump is more than big enough, its 14kW for an 12kW loss property, what could possibly go wrong" Well, it isn't a 14kW heat pump when it matters, when it's cold, it's more like 11kW, so quite a lot can go wrong when you need your heating the most. I think this may even be more common a problem than number 3 in your list, ie more people end up with undersized rather than oversized heat pumps.   

The one issue I've had with my install is checking that the we have the correct level of flow around the heating system before the install is performed.  So this may be related to pipe sizing or some other issue but surely this is the first thing to check before doing the install on a retrofit install

When say flow I mean litres per minute flowing through the system to the heat pump as different size heat pumps have different requirements. I don't mean flow temperatures just to be clear about my last comment 

Posted by: @soniks

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So this may be related to pipe sizing or some other issue but surely this is the first thing to check before doing the install on a retrofit install

And are there any unseen leaks, if it is an old system, and used to be open system with a feed tank in the loft, ie a pressure test. I accidentally had one, when my installer's plumber accidentally put full mains pressure on the secondary rad circuit, perhaps around 5 bar as the mains pressure is quite high here. It blew the 3 bar pressure release valve on the circuit, which made quite a bang, but after the 'pressure test' the circuit still maintains standard operating pressure, about 1 bar, for months at a time, so no leaks.

The same can't be said about the primary circuit, that does lose pressure over time. I suspect a small invisible leak somewhere... 

@cathoderay That's a difficult one to answer as I can't see any obvious signs of leeks but I do have to top up CH circuit more regularly than I think I should have too - maybe every 2 months and when I look at the pressure guage it does tend to vary through the day.  I did hear once when I was in the loft an air vent hissing and appears to be covered in some brown residue.  Is there any other reason air could fill in the system the circulating pumps may be?

Posted by: @allyfish

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4. "We'll leave the heating supply temperature set point high and the weather compensation disabled so you don't call us to complain the radiators are not hot" No matter that the homeowner/occupier will be paying nearly double in ASHP running costs from the day you drive off, but who cares as long as the phone doesn't ring. This has to stop, and it seems to be rather common.

5. "We'll put a 'touch this at your peril' sticker over the ASHP controller cover and hide the controller away in the garage or airing cupboard". After install, the person best placed to fine-tune and maximise the efficiency of the ASHP control is the homeowner/occupier. Only they will be able to correctly set the weather compensation based on experience of living in the property. Stop putting scare stickers on controls because you, the installer, cannot be bothered to invest the time to learn the basics and commission it properly, spend time with the homeowner/occupier and communicate that knowledge, or make a call-back visit to tweak the system.

My parents moved into a new build flat last year which was heated with a heat pump. There was basically no hand-over or instruction from the builders. The documents they were given for how the flat is designed to operate was absolutely laughable - it said that the heat pump was controlled by a powerful AI computer and that nobody should ever touch it. Meanwhile, the flow temperature was set to 60 degrees C!!! Presumably they meant to set the hot water to that (still too high), but couldn't be bothered to work out which was which and just put all the temps to 60. Radiators were lovely and warm though so my parents didn't complain... I've changed it to weather compensation and sensible flow temps that are a bit higher than the norm (they are old, they like it nice and toasty). But now every time I go over there I have to ask them if they're too hot or too cold, which is a difficult task for a "mustn't grumble" generation...

This is another aspect of the whole thing - it's one thing to regulate retrofits or installs where the homeowner actively desires one installed and can be expected to have done some level of research beforehand, but regulating new builds where the homeowner doesn't know anything about them, and the building company doesn't know anything about them - that's going to be a nightmare. And especially when those homeowners are elderly on a fixed pension and really REALLY need their home to be both warm and cost-effective.

Wow, 60degC flow temperature. There must be artificial intelligence there at work as there's no human intelligence. Great that you were able to fix it for them. You have to wonder how many people are crippled by massive electricity bills through similarly appalling commissioning. There are manufacturers who I'm convinced actually encourage installers to disable WC and set the flow temperature high to avoid the 'my radiators are not very warm' calls to their customer service centre.

The quantity of badly installed and commissioned ASHPs is probably on a par with badly installed and commissioned gas boilers, but no-one seems to notice bad gas boiler installs. As long as they heat the water to 70degC who cares if the condenser part never works or if the gas boiler is more than twice the size it needs to be. 

The new build ASHP market is an issue. The information given to the new buyer/tenant is non-existent, they don't know who installed it or who to contact to get help, etc. It will  be sold as an efficient green heating system (which it could and should be), but may be commissioned badly or inefficiently if any proper commissioning has been done at all. The whole UK domestic heating industry has to raise its game.

With the current state of play in the installer market - a homeowner has to take some responsibility for the install.

And they need to understand that beforehand.

The undersizing issue is real - I'm concerned my own is too small - 250m2 - Heat Loss Calc = 7.1kW @-1.5Deg = 10kW Grant Aerona (As calculated by grant, on a computer, without a visit)

But the real life scenario is that it doesn't seem to have the grunt when it is <5Deg and defrost cycling kicks in.

Also, manufacturers could make many things easier - the Aerona controller has far too many parameters - read/inst/User - the lists are long - and many will never be viewed or seen - a bluetooth connection, if not a wifi app, would also help to monitor. (All cost, I know)