Ok, so I had Grant out this morning, a really positive experience and knowledgeable installer (with a R290 at home).
He used a programmer (see photo) to update the firmware on the external unit.
The programmer doesn’t show the previous firmware, but seems like it may have been quite old.
Post install we had a new error “P21 Built-in DC water pump abnormal”, this appeared after each restart and the pump would only start if this error was cleared. Pump still ran at full pelt, but reattaching the pump controller cable fixed it. He was hear for almost 3 hours in total.
Heat pump now runs silently, the min and max settings now work, but I’m running currently with no limitations and it is totally silent.
Grant Eco300 was previously showing 83.3l/m and is now showing 3.3l/m. The flow meter is showing 11l/m down from a constant 24l/m or above.
System is now totally silent, all the previous noise was from the plant room and I think pump was running full tilt previously with the flow meter (the smallest option) and pipework acting as a limiter.
Very pleased with solution. And power usage (when no heat demand) is down over 75%.