During our visit, the customer mentioned he was having issues with his tankless water heater. After quickly trying to troubleshoot the unit, I was unable to figure out what was going on. I informed the customer that we would have to do a diagnostic check to provide solutions on fixing the unit. A full troubleshoot was completed with a Rheem tech. I found that the unit was experiencing low flow issues. Also the unit would occasionally show code 29, indicating a condensation issue. Considering the known codes, I made the customer aware that we would need to do a full service on the unit. We are scheduled to come back out tomorrow to flush the unit.