A broken Wall Sensor causes the Neato to go in circles turning away from a false phantom wall detection.
The complete assembly with bracket and cable is sometimes listed on ebay. The bracket may be different on older and newer Neato's.
The sensor itself is a Sharp electronics component, Sharp GP2Y0A51SK0F
Digi-key U.S. distributor
http://www.digikey.com/product-detail/e ... ow&site=us(with links to mfg data sheet etc.)
Also listed on ebay with a number of sellers in China where shipping to France can be cheaper than from the U.S.
The specific Sharp component is needed because there are several different ones made for different distance range detections; this is a short range model.
Be sure there is not simply a cable connection problem.
The sensor outputs a DC voltage around 0-3v changing with distance, higher as the target is closer. Red wire 5v supply, black ground, yellow sensor output. Check at both the sensor and at the system board end of the cable with a volt meter.
The cliff sensors use the same part. It is possible to replace a cliff sensor with an inactive resistor divider delivering the output voltage typical of floor detection, dividing say with 100K and 150K ohms (keep currents minimal, protect cpu) across the 5v line. Then the wall sensor can be fixed with the borrowed cliff sensor. Insure there are no cliffs to detect...
Robotshop.com Paris may have some Neato Robotics parts from the company.