Yeah. I wrote an article on the site about water mixing and me having a blending valve on the cylinder.

energy-stats.uk/hot-water-cy...

Immersion element? Legionella cycle? And perhaps the immersion is not being monitored by the electrical meter?

In the main it's a combined figure. But many installs, including mine are now splitting off heating and DHW COP. Open energy Mon provides the hardware to track and record this and now also provides the functionality in the charts and the app.

I have been thinking of an "Arotherm Basics" blog article. Will add it to the to-do list.

But really the installer should know everything I've passed on. But didn't? 🤷🏼‍♂️

Does the homeowner need to know every technical detail like this if installer did their job and handover?

You need to leave the system as open as possible. The more water in the system, the better the heat pump will run.

I went through this in my first winter and second winter. I wrote about automated TRV in this article.

energy-stats.uk/second-winte...

I have since ditched TRV entirely.

Head over to heatpumpmonitor.org?period=last3...

Loads of Vaillants being monitored over there.

Most getting COP 4 to 5+ in the past 30 days.

So i'd say 2 to 2.5 is very poor!!

Yes, it's a bit of a dark art.

Although weirdly, if you have the eBus controller, you can poke half settings into the WC setting.

Like 0.475

It does this because it can fall on half settings as part of auto adaptive WC setting.

Heat loss calcs in the main are oversized.
So whilst curve 1.0 in the book would be about right for 19.5C indoors (50C at -3), i'd start lower.

It's the old Heat Geek trick. Keep dropping the curve until you get cold. Then knock it back up one.

Inactive is purely weather comp

Active is WC with some room influence (I use this, i find it best)

Expanded works like Active but then also turns the heat pump on and off. I don't like this. More like a boiler control.

Final few questions for now.

What was the calculated heat loss of the house?
What did they say the design temperature was? ie 45C at -3C or similar?

Is the system 'open loop' (good) or do you have zones that switch on and off (bad, especially with third party stats/controls)

You can also find the COP from the heat pump controller, it's called Working Figure on there.

You can get separate readings for heating and DHW.

energy-stats.uk/how-to-measu...

That chart is from this article about Weather Comp Curves.

energy-stats.uk/vaillant-aro...

Do you have an outside temperature sensor?
Where is your internal sensocomfort located?
What Room Temp Mod setting are you on? (Inactive, active or enhanced?)
1.2 is pretty high. 0.7 seems better.
The Max setting is only a limiter. The weather curve will choose flow temp based on outside temp.