Vaillant inbuilt monitoring vs MID meters

Following the exchange between @dfeist , @Zarch and me in the Vaillant owners Thread, here’s some comparison data:

My system

Roughly a 1.2K constant offset between flow & return. This massively overstates heat generated in the Vaillant stats. My own (non MID, but properly calibrated together in an ice bath & sous vide) sensors work as expected.

@dfeist system

A 0.3K offset between flow & return but in the opposite direction than for my system, leading to an underestimation of delivered heat and thus COP. Heatmeter sensors work fine as flow&return are identical between cycles.


@Zarch system

Difference between Heat Meter and Ebus

  • Flow: around 0.3 & 0.4
  • Return: around 0.4 & 0.5

This would work out to a constant delta of around 0.1-0.2. Just from eyeballing it appears Vaillant would also slightly underestimate here.


If anyone else wants to contribute a similar graph I’d be happy to add it to the post.

@Zarch , @dfeist : If you don’t mind - could you also provide a snapshot of how flow rate compares for reference?