Greetings!A question about why the A320 isn't able to dump fuel came up at the chat on Tues. (Of course prompted by the recent incident at LAX.)
According to Mark (he just returned from England on his newly-minted 777 type rating), the ability to dump fuel is a design decision based on landing weight capability. Larger aircraft that have higher allowable take off weights than their max landing weight have the ability to dump fuel.
Smaller aircraft like the A320 (and 737) are rated to land with full fuel. The decision the LAX 320 made to fly around for three hours was safety-related (less fuel on board is less of a fire hazzard, it lightens the load on the wheels, and gives the crew time to troubleshoot and possibly fix the problem).
As for the malfunction itself, Mark says there have been several such incidents and all, as far as he knows, were maintenance related.
Hope that answers it.
Best!
Ben