The most likely culprits in this situation, check in this order-
1)Wrong power supply connected by mistake- Power supply should be labeled Tunze 5012.010
2) The pump speed was adjusted all the way to Max, back down the pump speed slightly, this error is caused by an overload, the pump is drawing too much power or the power supply is not supplying enough or too much.
3) The pump connectors are corroded, shorted (wet) or damaged.
1)Wrong power supply connected by mistake- Power supply should be labeled Tunze 5012.010
2) The pump speed was adjusted all the way to Max, back down the pump speed slightly, this error is caused by an overload, the pump is drawing too much power or the power supply is not supplying enough or too much.
3) The pump connectors are corroded, shorted (wet) or damaged.