Sounds like a fault in the 3-way valve (look for the T-shape in the plumbing). Some have a lever you can move manually to a detent postion. If you know what you're doing with electrical stuff it's not hard to replace the motor, which quite often dies. It detaches from the water side of things so there's no plumbing (unless the valve itself is jammed/ broken, which is less likely).
Colin, January 2010
