I have tried everything that Noritz teck has told me to do. Descaled unit, cleaned fan motor, had larger gas meter installed, set dip switches to 2 & 3. I am using 3" PVC pipe and the exhaust pipe in around 12 feet long with two elbows plus a rain cap. I may have a gas pressure issue and may need to get a manometer to check gas pressure at the unit. Before I go through that should I have the gas company come and check out the gas pressure coming into my unit? This has been an ongoing problem for over a year I keep resetting the unit and it will run ok for about 2 weeks then trigger a 90 code not any fun when you are taking a shower. I recently called Noritz again and was told that I could try to change the dip switches to 7 & 3 instead of 2 & 3 which it currently is. Not hopeful that will correct my problem but will try. Any help full comments would be appreciated.