In the main thermostats control the motorised valves, then the motorised valve controls the boiler, and it seems the main fault is the micro switch in the motorised valve fails.
With better systems the motorised valves are controlled with the on/off contacts in the thermostats, and the thermostats are set to master and slave and the master one connects to boiler turning it up and down rather than on/off, but although firms like EPH make these thermostats, they are not very common, you clearly don't have them fitted.
What many do is get rid of the hard wired motorised valves, and use TRV's instead, the electronic TRV is a motorised valve, and can connect to a hub or a thermostat or control boiler with the temperature of the return water.
Hive, Evohome, Wiser, Tado all have a system where the TRV's tell the wall thermostat to turn on/off. The twin motorised valve was a knee jerk reaction by the trade to satisfy government rules about being able to control zones within the home, electronic TRV heads also form zones, and more successfully that simply upper and lower floors.
Step one is work out what you have
Putting a number on every terminal helps, it seems likely 12 is to boiler, as orange cables which is likely from the micro switch in the motorised valve, but seems odd to be connected to blue wires.
16 looks like an earth, but 1 and 8 have green-yellow cables which should be earth, but also brown, which is normally line.
The regulations say "The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor and this combination shall not be used for any, other purpose." but it seems plumbers can't read, as found loads of green-and-yellow wires used by plumbers as lives.
That junction box looks like a nightmare, my house was the same, there is no quick fix, but in the main motorised valves come with the cables, so the colours from the motorised valves are normally correct, so you can start with that cable.
I worked out where each of my cables went, labelled them, then disconnected the lot and started again, but I did it in the summer when I had time, this is not the time of years to be re-wiring the central heating. Below is standard S Plan, you can see valve wire colours, orange and grey are the micro switches, you seem to have a grey at 7, but can't see second motorised valve.
If you have three zones, two for CH and one for DHW one would expect three motorised valves. I can only see one.
