how to fix air lock in peugeot 405 diesel water system?

There should be 3 bleeding points in the cooling system. 1 on the top right of the radiator, 1 on the thermostat housing at the right of the engine and 1 on the heater matrix usually on the left in front of the windscreen washer bottle. Try opening all 3 and let the engine tick over until bubbles and water emerge from all 3. Shut them all, let the engine tick over until the cooling fan cuts in and stop the engine.

Hope this helps!

JC
October 2009