Work Performed: Performed full maintenance and flush on 4-year-old Navien tankless water heater. Found water inlet filter clogged, restricting flow. Cleaned inlet filter, flushed heat exchanger, and verified normal operation. Performed maintenance on heater, including cleaning applicable screens and filters, and visual inspection of all components. Results: - Water flow restored to normal. - System operating within proper parameters after cleaning and flushing and maintenance . - No other issues found at this time.