Thanks for the GP12 Charge Pump Speed graphs. I was wondering if the pump speed might be really low (e.g. 20%) but it seems to always be over 50% while it’s heating - which isn’t crazy, but since the Charge pump is being ‘overtaken’ by the two Grundfos pumps it should be higher than 50%.
I would suggest trying a much higher speed while it’s heating. Mine typically goes to 100% (in ‘Auto’ mode) during a heating cycle, and it’s more like 60% during a DHW cycle, so there’s no issue with it handling a high speed. (The other option is to reduce the target DeltaT setting so it automatically runs the pump faster while heating. I changed my DeltaT from 7 to 4.)
30% pump speed while ‘Waiting’ is higher than it needs to be. I believe 30% is the default but a discussion on another NIBE thread settled on 10% as being more appropriate in most cases.
Another thing worth checking is the speed setting on the Grundfos pumps. Those are normally configurable into different modes and speed settings. If those were running less fast they would use less power and be better-matched to the Charge pump - although you will need to ensure you’re getting enough flow through the UFH manifolds (which hopefully have flow meters for each ‘zone’).
That fits with colder water being taken from the ‘Flow’ side of the Buffer to help supply the UFH circuits. Closing that valve would add more resistance to any flow from the Buffer, meaning more water would be taken from the Heat Pump instead.
That also makes sense: BT25 is getting a good share of ‘Return’ water mixed with the ‘Flow’ (and in Summer the ‘Return’ would be warmer, raising BT25).