Homeowners cascading tankless system had an error code. The main tankless was throwing the code, the second tankless was set to s5 instead of s1 to be the first tankless in the cascading system. Called the manufacturer and reset the system. Changes the main tankless to the left unit and cascading to the right. The middle is set to s1 and the right unit is s2. Tested and inspected the cold inlet filter and had no debris. Homeowner has a filtration system. Left a quote to flush the units.