The invention relates to a dosing pump unit for mixing a liquid reducing agent with an exhaust gas flow by means of a dosing pump which is connected, on the input side thereof, to a connection connectable to a reducing agent tank and, on the output side thereof, to a pressure pipe and a pipe for returning flow back to said reducing agent tank, wherein a non-return valve which is prestressed against a hydraulic pressure produced by the dosing pump is arranged in the pressure line, the return pipe is connected to the pressure pipe upstream of the non-return valve in the reducing agent flow direction and a first stop valve for selectively closing the return pipe is placed therein.