This is a more general query re above where most Vag cars now seem to have separate circuits for cylinder head and jacket cooling, the cylinder head stats opens at ~ 87C and the jacket stat ~ 97C, the  coolant temperature display/warning  comes from the cylinder head sensor, wonder what happens if the jacket stat failed and stayed shut, doesn't seem to be any sensor/alarm function for this?, general arrangement below. The lub oil temperature is monitored and can be displayed but I don't see anything in VAG com about any alarm function for this which at least might give a reasonable warning of jacket overheat?.

Two Stat Photos (Skoda).docx

Something else, it looks like the cylinder head thermostat opening is controlled by the return from the (cabin) heater?, there were dozens of posts on various sites re expansion tanks blowing out their water contents ( on engines even with only one stat I think) with no apparent high coolant temperature but replacing the heater matrix "cured" this as they were getting blocked and of course this would happen IF the heater return does control the thermostat opening, paradoxically, the more cabin heating required the lower the heater return temperature and the less the stat would open if the heater matrix partially blocked.