I don't know the exact model but our Hoover 8512 washer/dryer has a pressure switch near the top of the machine that senses the water level. This is connected by a tube to a small plastic reservoir at the back of the tub. If this tube gets blocked it causes the machine to overflow. Try removing this tube from the back of the tub and clean out any accumulation of washing powder and/or lime scale in the small plastic reservoir.
DML
March 2008