Sounds similar to my issue. Have you checked inside the pump to make sure there's nothing stuck in there? Also are you aware that if you hold down two control panel buttons at the same time you can operate the pump manually?
Like mine if it's worked ok for 5 years then it can't be the drain hose height issue. But the only thing I really did with mine was remove the olive pip from the pump and modify the drain. I'm still not 100% sure what the actual issue was but it's worked flawlessly ever since.
Good luck.