Well this gets even more interesting. A week ago, our system shut down with error C0-00, Flow Sensor. After the somewhat daft manual reset on the MMI, the unit started up again and was good for another two days when it shut down for the same reason again. Curiously a few minutes after the DHW schedule kicked in both times. Daikin attended today and replaced the sensor. They noted that the bypass valve next to the volumiser was wide open! I was wondering why it was struggling to hit dT 5 - it would at the lower flow rate but at the startup rate (even at 60%), it would struggle to reach 3. I can now hear a marked increase in flow through the radiators since Daikin made the change to the bypass valve. This appears to have reduced the initial flow rate down to 12lpm which I assume means the pump now has some resistance which it didn’t have before. I wonder if I’ll need to rebalance the radiators now. Thoughts?