Westinghouse WRG605IS blowing ELCB?

Hi
I woke up 1.30am last night and the power circuit had tripped The ELCB (Earth Leakage Circuit Breaker) had tripped. I went around slowly turning off every plugged in item and trying to reset the switch. I had all but given up when I remembered the Cooker Exhaust. I turned it off at the switch and the ELCB then reset.
I turned it back on at the switch and the power went again.

Just wondering what it could be as the item wasn't being used at the time. Just sitting there on standby ready to go. Its not electronic per say, just a light and 3 fan speeds when you pull the hood out at different intervals.