A door closer including: a body defining a chamber therein; a piston slidably supported within the chamber , and dividing the chamber into first and second cavities either side of the piston , which in use receive liquid; a biasing device for biasing the piston towards the first cavity ; a passageway connecting the first cavity to the second cavity for permitting the flow of fluid therebetween; a blocking member for controlling the flow of liquid through the passageway between the cavities; a moveable member moveable between first and second positions, wherein when the moveable member is in its first position the moveable member causes or permits the blocking member to assume a blocking position, thus preventing or at least inhibiting the flow of liquid from the first to the second cavity , and wherein when the moveable member is in its second position the moveable member causes or permits the blocking member to assume a non-blocking position, thus permitting the flow of liquid from the first to the second cavity ; and a permanent magnet and only one permanent magnet , said permanent magnet positioned adjacent or close to the moveable member for holding the moveable member in its first position; wherein the door closer includes a pole switching device and only one pole switching device , that can produce a magnetic field that is in opposition to the magnetic field of the permanent magnet to effectively cancel out or overcome the magnetic field of the permanent magnet and produce a net magnetic field that is either zero or in the opposite direction to the magnetic field of the permanent magnet so as to effect movement of the moveable member between its first and second positions. a body defining a chamber therein; a piston slidably supported within the chamber , and dividing the chamber into first and second cavities either side of the piston , which in use receive liquid; a biasing device for biasing the piston towards the first cavity ; a passageway connecting the first cavity to the second cavity for permitting the flow of fluid therebetween; a blocking member for controlling the flow of liquid through the passageway between the cavities; a moveable member moveable between first and second positions, wherein when the moveable member is in its first position the moveable member causes or permits the blocking member to assume a blocking position, thus preventing or at least inhibiting the flow of liquid from the first to the second cavity , and wherein when the moveable member is in its second position the moveable member causes or permits the blocking member to assume a non-blocking position, thus permitting the flow of liquid from the first to the second cavity ; and a permanent magnet and only one permanent magnet , said permanent magnet positioned adjacent or close to the moveable member for holding the moveable member in its first position; wherein the door closer includes a pole switching device and only one pole switching device , that can produce a magnetic field that is in opposition to the magnetic field of the permanent magnet to effectively cancel out or overcome the magnetic field of the permanent magnet and produce a net magnetic field that is either zero or in the opposite direction to the magnetic field of the permanent magnet so as to effect movement of the moveable member between its first and second positions. <EOS>