Overheated Whirlpool Inspirations ?

I just set my machine for a cool delicate wash. It took some time for it to get going and I just assumed there was a fault with the door, however, left it to run and it filled with water - I had it on half load. I forgot about it until I smelt very hot washing water and steam. Turned everything off, the front door was boiling, little water in drum is exceedingly hot. Door did open after a while but delicate clothes ruined due to exceedingly hot water. Any ideas?