Stannah 26 goes down but not up?

Our Stnnah 260 suddenly refused to motor up after sitting in the bottom rest position for a few hours without exhibiting any warning signs of a problem. Batteries check out ok, LED 9 flashing Green on pcb board showing software is working ok, no other pcb lights on, all mechanical functions eg stop siwtches etc have been checked. Charging lights 'on'. Manually wound it up and it motors down perfectly, any suggestions?