[shorod]

Welcome to the forum!

I have absolutely no experience with Citroens, but the cooling system is probably rather typical. As new as yours is, I'm expecting that it uses an electric cooling fan. When the engine is high on temperature, is the electric cooling fan running and moving air? Since the shop suspected the temp sensor, I'm wondering if they identified that the fan is not running. The temp sensor would have nothing to do with the engine actually overheating, unless it is preventing the fan from running.

Also, you mention that it overheats after you've been driving on the motorway. That makes me wonder if either the flow of coolant is insufficient (maybe due to a stuck or backward thermostat) or if the radiator is plugged or blocked or a hose is kinked somewhere. I'd be looking in to these types of issues, but these really are the basics. If your shop has not checked these already, you really should consider finding a different shop.

-Rod