Flushed (2) tankless units. Homeowner is having issues with cold water sandwiching. (Hot cold hot cold) and an error code 63 which is for low flow on record pump. I believe both issues are due to units not working together by a communication cables for all. Currently turned off one unit and valves off water. Tested by running water and currently the single unit is working as should. Will get pricing for communication cable from ringing rep and email over as well as sending over pricing on installing customer supplied 3 stage filter and spin down filter for incoming domestic cold water. The water heater on the right has noticeable corrosion on the internal record pump. Will gather information / parts needed to correct issue and email over an estimate. Homeowner to use chicken wire cut into circles to add to exhaust piping on exterior of home to prevent animals and debris from entering.