@glyn.hudson and I have been involved in a remedial project locally, a poorly performing LG high temp heatpump has been replaced with a Vaillant arotherm, the good news is that the COP has improved from 2.2 with the LG to 4.8 so far with the Vaillant 
It’s been interesting comparing the Vaillant app figures to the class 1 electric and class 2 heat meter that we provided to the installers. Here’s a screenshot from the app:
and comparison with electric and heat meter values:
| Vaillant app | Class 1 electric & Class 2 heat meter | Error | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Date | Electric | Space Heat | DHW | Combined | COP | Electric | Combined | COP | Electric | Heat | ||
| 29/03/24 | 30.4 | 175.1 | 7.9 | 183 | 6.0 | 30.1 | 144.8 | 4.8 | 1.12% | 26% | ||
| 30/03/24 | 21.9 | 100.1 | 16.9 | 117 | 5.3 | 21.9 | 94.4 | 4.3 | -0.15% | 24% | ||
| 31/03/24 | 14.4 | 91.1 | 1.8 | 92.9 | 6.5 | 14.0 | 73.3 | 5.3 | 3.20% | 27% | ||
| 01/04/24 | 19 | 107.7 | 5.7 | 113.4 | 6.0 | 19.0 | 90.9 | 4.8 | 0.18% | 25% | ||
| 02/04/24 | 13.3 | 77.4 | 6.3 | 83.7 | 6.3 | 13.4 | 67.0 | 5.0 | -0.46% | 25% |
The electric values are pretty good but looks like a temperature offset error is pushing up those heat values again. This has to be a relatively easy one for Vaillant to fix.
@glyn.hudson got some good pictures of the temperature sensors I think on his parents system, they look like they are in pockets and so should be good but perhaps they are just not calibrated pairs??