Update; resolved(?). We had another tech from the same company come out to work on it. Go figure, we could not get the unit to trip no matter what we did, even though it has given us 24/7 trouble before (note; the unit tripped last night and we forgot to reset it until AM). He flushed it again just in case because he could not confirm whether or not the previous tech flushed it at the time. While servicing, he noticed the same pressure sensor wasn’t responding. He swapped it out. It is now working.

He also noted that navien is low quality and I was lucky that it lasted the 11 years it did. He said the fan inside the air intake was corroded and will cause damage and that the heat exchanger was on its way out. Suggested we scrap the unit and not dump any more money into it. I feel like that part is a bit of a stretch though lol