It is possible for a return unit on a PF3W Digital Flow Sensor Manifold to reach its end of life.  This may be due to some accident such as excessive external force, contamination, or electrical malfunction.  If this happens, it is possible to replace an individual return unit for one lline without having to replace the entire manifold.  The return unit may consist of a flow sensor block with or without a flow adjustment or stop valve, a temperature sensor, or a combination.  Kits also include mounting screws and an O-ring seal.