1 of 2 Rheem Tankless water heater was flashing code P1. Homeowner moved in about a month ago and did not know of its service records. Went to flush both heaters but the one throwing the P1 code didn’t not have service valves installed on it. Flushed the heater we could and cleaned the filters in both heaters. Brought the issue of no service valves to the customer and the improper piping of the heaters and the customer decided that they would like the heaters repiped properly. Installed service valves and repiped the water lines in proper sequence. Flushed the water heater we could not flush earlier. Checked Kohler shower cartridge. It needs to be replaced in master bathroom