I’d really like to work out why the thing is falling over, but need to have a bit more of a think about how to debug it. I wonder if the meter manufacturer would have some comment.
Meanwhile having some way of ‘removing’ the DHW runs in OEM / the heat pump app would be useful. You could ‘sense’ DHW run by an optical sensor on the 3-way valve lever or temp sensor on the DHW tank flow?
Hotter water can hold less dissolved air. It will cavitate earlier.
It’s also possible that entrained air in dhw is simply not clearing the coil ever. I can’t comment on plumbing other than to say this issue is nowhere near as prevalent in the district heading space.
The manufacturer is following the mbus standard here so had already told you everything that you need to know there.
The error values displayed are being incorrectly parsed by the mbus parser. These are NOT the same register as the regular values. Get a proper mbus parser and you’ll see that they have different names and can be parsed/filtered accordingly.
Perhaps there is a way to get the vaillant control box to circulate water through the DHW coil for an extended period (say 24h). I have an auto air bleed valve on the coil flow so it should eventually work the air out of the coil…
Or run. Stop. (for air bubbles to consolidate and move to the top of the coil) Run. Stop. Run. Stop.
(whilst it is running the air will be entrained)
Does your auto air vent function / is it open? You’d usually open these during initial system commissioning them close the cap afterwards - to avoid any fault in the AAV pishing water everywhere whilst you’re not actively watching it.