I have the same problem as Dave. My seagull pro is about 2 months old. I have only seen it clean walls twice (first month) when in wall+floor mode. I didnt think much of it at first. When I wanted to try the only clean-wall mode recently, the green lights automatically switched off when the knob was turned to that mode. I tried many times on different days, turning knob back to power off, then turn to the 3rd mode again. Same result, the machine just shut down when turned to wall-only mode. Why is that?
(By the way, my pool is rectangular shape, no slope or steps.)
Hope to hear a reply soon. Thanks.