The blackboard needs cleaning. = The blackboard needs to be cleaned. 黑板需要擦干净。

The broken window wants repairing. = The broken window wants to be repaired. 那个破窗户需要修理。

另外注意be worth及be worthy 的用法：

The problem is worth discussing.

The problem is worthy of being discussed.

The problem is worthy to be discussed.

以上三个句子都意为"这个问题值得讨论"。