Hi! Yes, it's three years ago that we had this trouble on the Xsara Hdi. I decided to get a replacement sender from the local agent - as Mart said, it cost £9. Not too difficult to change. A few bits of pipe work to remove, a U-shaped clip to pull out, and the sender just pulls out. There's a loss of coolant which needs replacing and bleeding, but since changing it, there's been no further trouble.