Showed up to customers home to perform a Navien water heater service. Removed the air intake filter screen along with the drain trap and cleaned it off. Flushed the hot and cold water lines. Removed and inspected the igniter. Cleaned the flame sensor. Exercised the two pressure relief valves. One of the valves would not close and seal properly. Called Joe and Susan to show the findings. Pulled up a replacement estimate and they agreed to have the repair done. Took full payment for the repair from Joe. Drove out to the supply house to pick up parts. Came back to the job to shut down and drain the unit. Replaced the relief valve and checked for leaks. Fired up the unit. All is good, no more leaks. Customer was very upset with the initial expense incurred. I explained the situation in detail and she reluctantly agreed to the repair. Job completed.