I've only just fixed the same problem on my daughter's Peugeot 306!
The pump was making no sound. I pulled the electrical connector from the pump (pressing in the wire retaining clip as I did so) then connected a 12 volt bulb across the feed connections. My daughter pressed the wash/wipe switch and the bulb lit, confirming that a supply was getting to the pump.
I then used an old trick. After refitting the electrical connector, I got my daughter to keep dabbing the switch to give 'jolts' of power to the pump whilst I repeatedly tapped its side with a small hammer.
After about a minute of that treatment, the pump started working again. I advised my daughter to use the pump every couple of days during the cold weather to help keep it free.
David W., December 2010