Universal Descaling Method. Hi, for Descaling any tank less water heater you need these tools, 1. spanner 🔧, 2. Soft water pipes (2 pieces) 3 feet each. 3. Soft disposable Gloves. 4. Small amount of Drain Opener Liquid, we use to clean commode and Sinks. (i.e Harpic, Sweep) ----First of all you have to Close water supply valve to the water heater, and unscrew W.Heater main inlet and outlet Screw, -----then attach 1 external soft water pipe to outlet connector and 2nd to inlet connector of w.heater. ---Now Put some drain liquid in inlet attached soft pipe, ----for pushing water flow towards w.heater, attaching to any tap and slow release water to pass through the heater, it will clear scale you can repeat 3 or 4 time for best results. Don't forget to keep outlet pipe in a plastic bag or bin. For safety purposes. After that leave clean water to pass through heater to remove drain liquid.