Customers tried doing yearly flush on tankless Navien. Customer could not find O ring that went on dirt trap located on bottom of tankless itself which caused a leak. Upon arrival got down and located O ring that was jammed in top of dirt trap. After fishing out O ring and reapplying O ring to seal. Tested by turning water back on and everything is testing OK at this time. Informed customer that they Can have service yearly on tank flush itself. Thank you for choosing LBA and have a wonderful day!