After your post and assuming the worst, I've just spent some time testing both Mira showers. There's a definite range of cold to hot when turning the temperature control, so they appear to be working fine, it's just that the "hot" setting is now around 9 when it used to be 5.
It reminded me that it's possible to change these, so out with the screwdriver and I took the front of the dial off and adjusted it, so now it is in position 5 at the expected shower temperature rather than at 8. Both showers temperature settings now seem to be around where they used to be!
Unfortunately, the new digital shower hasn't been used yet (apart from testing) as we are still awaiting the new shower enclosure, which won't be in stock until February.
So, with the water temp now set to 60 deg C and the shower temp gauges adjusted, things should be back to normal, assuming the hot water takes less than 30 minutes to heat up in the morning, allowing at least 30 mins to start warming up the house (boiler is timed to come on an hour before we get up).
Interestingly (or not), after testing the showers, I noticed the system was in DHW mode (not surprisingly), but the boiler was showing status S.53 (Appliance is within the waiting period of the operation block function due to water shortage (VL-RL spread too big). I haven't noticed this one before. Everything still seemed to be working as normal (external and boiler pump on, cylinder valve open, gas burner on).
Went back to the boiler 10 minutes later and it was showing S.31 (Central heating thermostat knob turned off or no heat demand by the eBUS control unit). Again, not seen this before! At this point nothing is on, but that's not surprising as according to the VRC 700 the system is in standby as there's no demand for heating or hot water. Ah well, I'll assume all is well as this is obviously a "status" code, not an "error" code.