What does Ls and Lr mean? November 30, 2018 02:51 Updated Follow Ls means live supply so this is where you put 230v or 24v into the switching circuit on the device. Lr is the switch live return back to operate your system. These connections are electrically isolated from the main board to prevent back feed. Related articles What cables do I need to connect my thermostats? How do I wire a manifold valve to my UH4 The output is volt free what does this mean? How do radiator zones on the Heatmiser wiring centres enable the boiler? Can the UH8 work with 2 port valves and provide a volt free boiler enable switch?