@pash44pump - good, we're on the same page (screen) on the wired controller. As you can see from the chart I posted earlier, the LWT/RWT often vary a lot over time, meaning a spot reading doesn't tell us very much. I can't remember whether that hideous Midea app (if you have it - if you don't, don't bother) records and so can chart LWT. If not it is either get out a deck chair and sit by the wired controller for an hour when the heat pump is running, or finding some other way of getting the actual LWT over time.

That is a lot of not well insulated external pipework. Is there any reason why it can't get inside the heated part of the building sooner? I suspect the physical location of the heat pump doesn't help either, but better than in the middle of the lawn I suppose. Nonetheless people do sometimes have very long outside pipework runs. Extra insulation is probably the key thing to get right. @transparent may have some suggestions.

Fwiw...  I set up my weather compensation on LG heat pump... starting with nil base knowledge.

However the initial change was very easy and took less than one hour:

1. Changed the controller setting to use the pre-set weather compensation setting
2. Changed internal programmer controls so that heating is on 24x7 
3. Changed internal thermostats to high levels to ensure 24x7 throughput
4. Opened all TRVs to max

That basic setup probably achieved 90% of the setup and we could've simply stopped there.

But for best efficiency and comfort further tweaks will typically be required

1. Adjust the wc curve slowly (perhaps one degree every few days) by trial and error to get the curve as low as possible. 
2. Consider using thermostat setbacks overnight but avoid setting back too much (takes a long time to heat back up). Because we're on Intelligent Go with 7p kwh overnight rate we actually INCREASE our target temp overnight which reduces heat demand in the day. Similarly heating hot water to higher temp at night.

Many users of wc recommend avoiding programmers and thermostats completely - which I don't disagree with. Except in my case with batteries and time of use tariff a bit of tweaking with programmer & thermostats works for me - such tweaking is not necessary for many people.

@cathoderay thanks. I've always thought the same - I have no idea why they ran it outside. It can easily go straight into the building and I have someone coming (not original installer) to have a look at costs later this week. I'm not sure if it will be cost effective though - let's wait and see.

Advice from others on what product to use to insulate if it does stay outside would be welcome. At the moment it has gaps at the back and the cable ties cut into the foam making it less effective. I must be losing an amount of heat in very cold weather particularly (which is why I wondered if in/out temps came before pipes i.e. from inside heat pump or post pipes within the house). 

@tim441 - an excellent succinct summary.

@pash44pump - re-routing the pipework may well make sense, a one off cost vs a never-ending drip drip drip of heat loss costs into the garden. It will obviously depend on costs. I'm hoping @transparent will chip in with some thoughts sooner or later, what he doesn't know about these things probably isn't worth knowing.

Posted by: @cathoderay

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people do sometimes have very long outside pipework runs. Extra insulation is probably the key thing to get right.

Thanks for the nudge.

In some places I'm struggling to see any attempt at pipe insulation.

As for the external runs:

This isn't external insulation at all.

There are pits in it which allows ingress of water.
The cells (bubbles) from which it's formed, must be 'closed'.

It should be UV-resistant and have a smooth external surface.
This is often referred to as Solar Insulation.
It first appeared in the days when solar-thermal panels were being roof-mounted.

Have a look at this Kaiflex product, sold by BES

Armaflex is a similar, rival product.

Both companies make a 3mm thick tape which wraps around joins in the lengths of insulation:

All joins should, in any case, be 'welded' with Impact Adhesive applied to both faces of the joint.
Make sure it's touch-dry before pressing the sides together.

Nylon cable ties shouldn't be present on insulation runs.
They compress the wall thickness, leading to cold-spots,
and also cause gaps at bends, which are difficult to glue closed.

To fix an insulated pipe-run in place, use a Munson Ring outside of the insulation.

Most manufacturers have standardised on using M10 threaded (brass) rod between the ring and the base-plate.
It's the diameter of the ring which changes according to the external diameter of the pipe insulation.

There shouldn't be any pipe clips with insulation cut around them!

Insulation needs to extend completely over all valves, whether outside or inside the property.
That's what the larger-diameter insulation sizes are for!
For external runs, check that the larger diameter length is glued to the smaller pipe insulation, preferably by over-lapping it.

There must be no gap for rain to enter between the pipe and its insulation.
That's especially important where the pipes join to the heat-pump itself.

Having rainwater running next to the pipe simply sucks out the heat, and throws it away on the ground below!