the good news first - it is a DIY job and can be done through the engine inspection grill, no need to remove the inlet manifold.
The engine cover needs to be removed only to reach the bleeding point in the engine bay to bleed the cooling system afterwards.
This is the part we need to access - the thermostat housing:
To get access I removed two elements, the coolant expansion tank and the oil neck.
The oil neck is fixed with one 10mm bolt only to the inlet manifold.
The expansion tank is bolted on with two 8mm bolts, two rubber hoses are fixed with clamps. Of course you will lose some coolant when removing the lower hose but it can be caught easily with a little bowl and reused later:
And this is the area we need to access:
The thermostat housing is bolted to the engine with a single 10mm bolt, quite easy to reach (but hard to photograph).
One rubber hose is clamped to it, also easy to reach and remove. Here you will lose about 3ltr coolant, catch it with a bigger bowl under the car.
Now the funny part starts - to remove the thermostat housing a coolant hose needs to be moved that is bolted to the engine.
It's not rubber but steel and the bolts cannot be seen from above. The area is really narrow with several hoses and cables, small hands and several extensions for a ratchet are an advantage...
That's the part that needs to be moved:
It's bolted to the engine block with two 10mm bolts you need to find with your fingertips...
That's the hardest job!
When the bolts are lose the hose can be moved to the left and the thermostat housing removed.
To open the housing simply open three 8mm bolts and remove the thermostat:
The thermostat did not look too bad but when tested in boiling and cold water it did not open/close.
Rebuild in reverse order,
refill the coolant system and bleed afterwards.