Navien tankless water heater maintenance and inspection. Performed flush on the tankless with descaler solution. Inspected and cleaned internal water filter, air filter and condensation trap. Found moderate buildup of dust etc. on air filter, Large amount of calcium buildup on water filter, about half plugged, would have put a lot of strain on the system if it can only allow half the proper flow of water through itself. Highly recommend getting tankless serviced more frequently, it is recommended to do it at least every two years to avoid overworking or damaging the system. After completion of maintenance tankless is working well, no concerns at this time.