According to a 418 page manual I read there are 2 possibilities for this fault. 1. Directional limit tripped while the valve coil is picked/energized. 2. Mother board component u78 is bad and generating false signal.. So we have gone through all the HW switches and adjusted the UP final further away from the landing by 1/2" incase the unit it intermittently leveling through or shooting through the floor.. We will see how it goes.