Likewise cars, they always go wrong eventually so I just walk everywhere.
Having now, finally started to look properly, of course you are right Mark. In theory, we only need to replace the thermostatic mixers. But not sure how easy that is going to be. For example, one of our showers has a mixer that is rectangular, feeding into a square riser with a square shower head.
May I check first of all, do all thermostatic mixers have the same distance between the hot and cold water inlets?
As far as I know, it’s a fairly standard measurement - 150 mm ? (but easy to check). We used to have a square profile mixer, but the outlet was round (with a standard round screw on fitting)
Most are now 150mm but there are odd ones out there. Also adapters to make older versions fit even if they are a bit of a fiddle to fix, loctite keeps them in place.