Please check the impeller first, a common culprit is that the impeller has seperated from the magnet, you will find the magnet has a grey base of plastic that may have broken off and this will allow the magnet to run without turning the impeller. This is part 0800.042 and can be ordered on Tunze.com. The pump is part 0800.040, it can ber ordered on Tunze.com and Premium Aquatics will also have them in stock.