So we might expect COP around 3.5 and therefore draw around 4.5kwh?

I think I occasionally see that sort of draw in winter - especially if heating DHW to higher temperatures. But I believe my "normal" usage running the heating on AI is running around half that - or less.

I can see my annual use is 5800kwh for heat pump as it has a dedicated meter. Peak months around 1000kwh so perhaps averages 30kwh per day. But of course coldest days if freezing temps day and night we might use say 80kwh?

I don't monitor day by day - only monthly. We are in SW England where winter is generally relatively mild.

I tried quiet mode (it is still in it) and I also put the current limiter. Before that when it started it had peaks of 6(!) kW, now only 4.5.

@jamespa I run 24x7 with weather compensation. So flow temps will normally increase at night

Thats true.  Ideally the FT could go up a bit further ie above the level required simply to sustain target indoor temperature, but not all heat pumps support this; fortunately with a night time cheap rate the tarrif lows and the consumption highs coincide naturally!

As my ashp was a retrofit I use simple digital thermostats to manage the target temp increase overnight. 

As it works for your case that's great.  My only reservation (in the more general case) is if thermostats are causing daytime cycling.  That's why the recommendation is generally to set them a couple of degrees above the target so that they act as limiters not controllers.  

Everything in this game is a bit house and person specific, the best general approach is almost certainly to start somewhere generically sensible, and tweak if there is a good reason.  Unfortunately plenty of heat pump setups reported here (which of course is a distorted subset of the total population) dont start somewhere sensible!

One option in LG is to run in Silent/Quiet mode. I don't use it but know others have .. quite successfully reducing cycling.

Personally I'd go for weather compensation as priority .. its a chicken & egg thing! With WC set changes should become clearer.

As my ashp was a retrofit I use simple digital thermostats to manage the target temp increase overnight. 

Afaik havenwise is a bit limited on compatibility and while Homely supports many more they don't support my 2020 installed LG. I guess both are worth considering if compatible.

I think I've got my setup reasonably good now after a few years:

1. Move to weather compensation

2. Reduced daytime DHW target temps with higher temps scheduled overnight

3. Use higher temp targets overnight for room temp to maximise cheap overnight tariff

4. Best time of use tariff (in my case Octopus Intelligent Go) ... linked to zappi charger and ev

5. Maximise IOG to fill batteries at night. I use WonderWatt to help with that (again only suited to certain compatibilities)

6. Export solar prod + force discharge batteries outside of heating season.

So inevitably it very much depends on setup,  usage, tech saviness, etc etc. This forum has helped a lot with understanding options & questions to ask!

Correct me if I'm wrong, but if I'm running the heat pump at fixed 37° flow temperature, with the outside temperature varying between 4° and 17°, I think that, at the very least, I should get the COP corresponding to 37° flow with 4° outside. But, according to my measurements, I'm getting way less than that.

Yes you should, or thereabouts, but only if you are operating without thermostats or TRVs.  If you have a thermostat constantly cycling it on and off, or TRVs/zone valves shutting down much of the system, then you will almost certainly achieve a COP which is poorer, possibly quite a lot poorer, depending on how it is working.  Worst of all is a 'smart' thermostat with 'proportional' control, they can really knacker heat pump performance.

I knew of the importance of weather compensation but I wanted to identify and solve the problems with the system that I think are there before adding other variables to it.

My initial reaction was fair enough.  On second thoughts (and referring to the above) its almost impossible (exception - a very low temp UFH system) for a heat pump to be working properly without WC and the house to be simultaneously comfortable, simply because of the need to match emitter output to demand.

There isnt that much that can go wrong with a heat pump system, unless the heat pump itself is at fault, which is pretty rare.  The principal issues are

• substantially oversized (and thus cycles a lot and/or operates permanently at an inefficient part of the compressor curve)
• presence of buffer, low loss header, or plate heat exchanger between heat pump and emitters, or mixers if you have UFH
• pipework restrictions/inadequate primary flow/blocked filters
• undersized emitters
• overuse of external controls, most particularly smart stats like Hive and TRVs
• incorrectly adjusted weather compensation
• poor insulation of primary pipework

Combinations of these are not unknown and that can really mess things up!

Correct me if I'm wrong, but if I'm running the heat pump at fixed 37° flow temperature, with the outside temperature varying between 4° and 17°, I think that, at the very least, I should get the COP corresponding to 37° flow with 4° outside. But, according to my measurements, I'm getting way less than that.

I know there is a lot to set and tweak, but I would like to start from a known good system/installation. For example I can set the flow temperature to rise a bit when there is overproduction of photovoltaics (I have a 10kw array). Very rare in winter but during autumn should happen more.

Right now I'm a bit at a loss, that's way I want to gather more data.

1. With Intelligent Go overnight tariff just 7p it makes sense for us to INCREASE temps overnight (opposite of setback). In our case by 1 deg

2. Similarly we heat hot water at night on a schedule to 50deg (with top up daytime heating just 40deg if necessary). In any case hot water can have a lower target for most people - try 47deg at first and then tweak lower if possible. Will be more than sufficient for most households - unless several teenagers!

Agreed with the one qualification that increasing the nighttime temperature should ideally be done by increasing the flow temperature at night not by reducing/controlling the daytime temp using a thermostat. 

Some heat pumps allow you to do this, some don't.  For ones that don't it may be better just to operate at the same temperature 24*7, or get either homely or havewise to do it for you.

1. With Intelligent Go overnight tariff just 7p it makes sense for us to INCREASE temps overnight (opposite of setback). In our case by 1 deg

2. Similarly we heat hot water at night on a schedule to 50deg (with top up daytime heating just 40deg if necessary). In any case hot water can have a lower target for most people - try 47deg at first and then tweak lower if possible. Will be more than sufficient for most households - unless several teenagers!