For unknown reasons Samsung front loaders will sometimes take a long time sensing. How long have you let it run after starting? I've seen 7-8 min of sensing when other times it fills almost immediately.

Quick test on these is easy to enter. Press spin, soil, and power at the same time and it will go into test mode. Rotate knob until it says test. It won't open a valve unless door us locked, I think its the button next to temp that locks it. Once it's locked every time you press the temp key you'll open a different valve. Verify all valves work. It'll max out at some point and you'll need to find which button drains it. It'll be to the right of the temp key. Or you can turn knob one click to spin and it'll drain first. There may be a tech sheet taped to the back to help in what I can't remember.