Homeowner had Navien tankless water heater that was not working and had coded out. Upon arrival I inspected and found water leaking from around the condensate line. The unit was gurgling and sounded like the condensation line was blocked. I found the line was going through the crawlspace and then the water filter was connected. This was all on a 1/2” line. Additionally the unit was missing a thermal expansion tank. I recommended adding isolation valves for serviceability. This would allow for the unit to be worked on without shutting off water to the whole house. The homeowner decided to move forward with all of the work. I tested everything and verified operation. The tankless unit had built up a fair amount of water inside the cabinet. I did remove water from the gas air intake. The unit was whistling at times which could be that the water needs to evaporate out of the cabinet. I left the front panel off and the homeowner is going to call if noise persists.