Everything.
The electrics to the fuel pump burned through, so the car wouldn't start. This happened a total of three times.
The water drain just in front of the windscreen became blocked, which soaked the floor and came in as steam through the heating system.
It let me down in April, June, July, September, October and December. Once every two months. The final time was the head gasket, when I was advised to sell it by my mechanic. He said:
"The odometer might say it's done 99k, but since the head gasket's blown, it might as well have done 250k. Sell it, or you're just asking for trouble".
So I did.
OK, it's comfortable, reasonably quick for a diesel, but the engine is fairly loud and unrefined.
It handles OK, but has a tendency to slide, which is made worse by there being practically no feedback through the steering wheel.
The built-in stereo and speakers are terribly tinny, and if you lose the stereo code, Citroen charge £25 to find it for you.
This is my second Citroen - I thought I'd give them another chance after my first blew up. Never again. I'm sticking to Japanese or German!
In regard to the radio code issue. I popped in to S. E Thomas in Godalming(Surrey) and the service advisor gave me the code for free. What a nice man!