A blood treatment device comprising: a dialyser; a flow balance pump and valve arrangement comprising: a first pump for delivering a volume of cleaning solution from a cleaning solution source to the dialyser; a second pump for removing a volume of cleaning solution from the dialyser and delivering said cleaning solution to a drain; a first dialyser inlet valve arranged between the first pump and an inlet of the dialyser, and; a first dialyser outlet valve arranged between an outlet of the dialyser and the second pump; wherein the first pump and second pump are both operable to deliver a volume of cleaning solution from a cleaning solution source to the dialyser and remove a volume of cleaning solution from the dialyser and deliver said cleaning solution to a drain; the device further comprising a second dialyser inlet valve arranged between the second pump and the inlet of the dialyser and a second dialyser outlet valve arranged between the outlet of the dialyser and the first pump, wherein each of the valves and the pumps of the flow balance pump and valve arrangement are independently operable; and wherein the blood treatment device further comprises: a control system configured to operate the flow balance pump and valve arrangement in at least one first mode permitting haemodialysis and at least one second mode permitting haemodiafiltration. a dialyser; a flow balance pump and valve arrangement comprising: a first pump for delivering a volume of cleaning solution from a cleaning solution source to the dialyser; a second pump for removing a volume of cleaning solution from the dialyser and delivering said cleaning solution to a drain; a first dialyser inlet valve arranged between the first pump and an inlet of the dialyser, and; a first dialyser outlet valve arranged between an outlet of the dialyser and the second pump; wherein the first pump and second pump are both operable to deliver a volume of cleaning solution from a cleaning solution source to the dialyser and remove a volume of cleaning solution from the dialyser and deliver said cleaning solution to a drain; the device further comprising a second dialyser inlet valve arranged between the second pump and the inlet of the dialyser and a second dialyser outlet valve arranged between the outlet of the dialyser and the first pump, wherein each of the valves and the pumps of the flow balance pump and valve arrangement are independently operable; and wherein the blood treatment device further comprises: a control system configured to operate the flow balance pump and valve arrangement in at least one first mode permitting haemodialysis and at least one second mode permitting haemodiafiltration. a first pump for delivering a volume of cleaning solution from a cleaning solution source to the dialyser; a second pump for removing a volume of cleaning solution from the dialyser and delivering said cleaning solution to a drain; a first dialyser inlet valve arranged between the first pump and an inlet of the dialyser, and; a first dialyser outlet valve arranged between an outlet of the dialyser and the second pump; wherein the first pump and second pump are both operable to deliver a volume of cleaning solution from a cleaning solution source to the dialyser and remove a volume of cleaning solution from the dialyser and deliver said cleaning solution to a drain; the device further comprising a second dialyser inlet valve arranged between the second pump and the inlet of the dialyser and a second dialyser outlet valve arranged between the outlet of the dialyser and the first pump, wherein each of the valves and the pumps of the flow balance pump and valve arrangement are independently operable; and wherein the blood treatment device further comprises: a control system configured to operate the flow balance pump and valve arrangement in at least one first mode permitting haemodialysis and at least one second mode permitting haemodiafiltration.