During my visit, the customer mentioned their water heater was not producing hot water. The Navien tankless was showing a E.438 error code. I spent some time troubleshooting the unit. I realized the unit was not sensing water flow, and the recirculating pump was not working. I then called the Navien tankless support team. The tech walked me through a few parameters. I also removed the flow sensor and found plastic lodged into the impeller. I was able to remove the plastic but this did not fix the issue. The recirculating pump was also getting voltage but was not coming on. I later found out that the internal check valve failed and the pieces were scattered through the unit. I spoke with the customer about options moving forward. She decided to replace the unit. A new Navien 240-A2 was installed, replacing the old 240-A. An ionizer was added on the cold water along an expansion tank. The ionizer allows for a 5 year maintenance instead of annually. A new pressure reducing valve and ma