Indesit washer dryer soap drawer keeps filling up with water?

My Indesit washer dryer soap drawer constantly has water pouring into it - not at the speed of when it is on the wash cycle when it's getting the soap powder, but still quite a good flow.

This then runs into the washing machine drum, so the washing is sopping wet even after a drying cycle. The drum continues to fill up with water and I dread to think what would have happened if i'd not spotted it this morning.

The water still pours into the drawer even when the washing machine is turned off (didn't get as far as turning the mains power off) so i've turned the water off at the wall. Turning the hot water flow to the washing machine stopped the leaking. The cold made no difference.

Anyone got any ideas on what might be causing this? Is there a valve that controls the flow of water to the draw that might be wedged open a little? Is it something I can fix myself?

Thanks in advance :)
Emma