The Daikin integration exposes sensors that match the ONECTA app or MMI; so for me that means incorrect electricity consumption.

ESPaltherma is much lower level, but the electricity (voltage and current) sensors are considered inaccurate, so people seem to be using external monitoring. I’ve got a CT clamp around the heat pump feed that goes back to an Eddi, then I collect the data in HA. 

If you want to get going with ESPAltherma, there’s an excellent guide here:

https://community.openenergymonitor.org/t/daikin-altherma-espaltherma-home-assistant-with-openenergymonitor/25057/6

Have you set up any home automation or smart steering of your heat pump?

I haven’t found a fix for this. I mentioned it to Octopus and a Daikin engineer when they visited and they were not very interested, stating that it was only approximate anyway. 

So I setup ESPAltherma and have had it running for 3 months with Home Assistant:

https://raomin.github.io/ESPAltherma/

It is excellent and provides great insight into what your Daikin is doing. 

Did anyone try to access the Onecta API directly? So not through the app or via the MMI, but directly in the API. 

My unit has started doing the very same thing since last week. I can't seem to be able to get any answers on how to resolve it.

Thanks.

According to the system it only produced 10,000 kWh of heat in a year, at a COP of 2.6. My heat loss calculations suggest it should be more like 14,000 kWh which would make the COP more like 3.6.

As for the "electricity in", my installer fitted a separate meter on the incoming supply, and it agrees pretty closely with what the unit thinks it has used (4425 kWh since installation on the external meter, versus 4441 kWh on the unit display).