Yes I have restarted HA.
Well God knows why but I’ve restarted HA for the 5th or 6th time and now the old node has finally disappeared and the new “hot_water_temp” entity is available.
Thanks for trying to help everyone - much appreciated (although it remains a bit of a mystery). Everything is now as it should be but I don’t really know why.
Thank you so much guys, I had the very same problem for over a week - with this I could finally resolve it! 