Where did you get it from? Contact them I'm sure they will give you another one.Bought a wave maker of theirs and 6 months later it's dead. I guess that's what you get when you go cheap.
Contact the buyer or the manufacturer with proof of purchase an online receipt will do. Trust me most companies will do you right especially the bigger ones.Amazon
It seems like it maybe due to buildup and not the actual product going bad. You said it yourself it started working. If anything gets clogged in there its not the product its just how things go in this hobby. What I do with pumps that get clogged I just open everything up and make sure everything is free from debris and propeller is working. Inside the cover you can put some sponge in there so bigger particles won't actually break or stop the circulation.The seller has asked me to diagnose on my own and if I cannot fix, to send it back and they will fix it. I have to pay for shipping though.
I have extremely hard water, so decided to clean it in a vinegar solution as there was a ton of grime. It started working but stopped overnight again. Will give it another shot and then look into the cost to send it back.