Arrived on site and customer stated his heater displayed a code 05. The Heater was an “Engine” Rinnai Water heater/tankless combo. I went ahead and got on the phone with tech support , and they confirmed with me that the error code 5 was a code indicating that the filter on the unit needed to be cleaned and cleared of debri. Once I removed the filter and cleaned , I let the heater run for 15 minutes to ensure no error code appeared. I also provided options for the customer to install a new tankless heater and tank options, as unit carries no warranty’s or warranty’s on repairs .