Quick update, things appear to be working! It's now been several days with no overshoots, so what did I do?
- I removed and reinserted the insertion probe into the water cylinder to ensure it was fully seated.
- I moved the EvoTouch controller into our Living Room so that it is almost directly below the airing cupboard where the water cylinder is located.
At this stage, I'm going with moving the controller having made the difference, why? When I looked back through the temperature logs, I noticed the overshoots didn't start appearing until I moved the controller into our hallway onto the wall amount. At the same time as wall mounting the controller I also tidied up the temporary wiring in our airing cupboard, and also wall mounted the BDR91's, and CS92A controller so lots of changes at once!
I'm going to leave the controller as-is for another week or so. I'll report back again then with my findings. Oddly, which is why I'm still slightly dubious, I'd already tried moving the controller onto our landing so that it was a lot closer to the airing cupboard before but this appeared to make no difference. Maybe the signal is travelling better through the floor.