Hi Zute.
Normally the TD5 temp gauge ONLY reads at the middle unless its overheated and too late.
Run the vehicle with the climate control switched off.See if the electric booster fan in front of the radiator is running.
If it is the ECU has registered overheating and is protecting the engine,it will remain till the fault is cleared.
You are in luck,we have an esteemed member in Alice that fixes Landys for a living.
Im sure he will be onto this real quick
Andrew