For the first time I turned to the Navien service center and was just stunned)) I bought the boiler more than 2 years ago and it is still under warranty.
I called Kabanbai Batyr 260a and that's what they answered me...
I live in Mukhametzhan Tuimebayeva, it's 10 km from the edge of the city and 21 km from the center. They said that the check-out and diagnostics are free, but in my case, the check-out will be paid.
After 10 minutes, they called back and said that they were not making a trip to my village. That's it! Probably it is necessary to remove the boiler and take it for diagnostics. But when they sold, they did not warn that they would serve only in the city.
Maybe there are masters who do not work in the Navien service?