The gas, fire, electrical, structural etc. Building Codes have been written after investigations of deaths, injuries, fires. There is no other reasons to have codes. The three little pigs' out the importance of structural codes.
I contracted my house and was very involved in the process. I carefully selected the companies to deal with. Afterward, I counted the number of guys that worked on the house. There were 73. I had to deal with intoxicated and drunk tradesmen and FIRED 3 crews totally and did not pay them. On the remaining crews I had 3 people declared unwelcome for drug or alcohol use. on site. Two of those were subsequently fired by their employer. The inspector caught 3 electrical deficiencies. The electricians onsite were a Master, a journeyman and an apprentice and they made a mistake. The venting on the furnace was wrong. They were journeyman and apprentice gasfitters. I am not going to go on about all the problems with "professional tradesmen" Of all the trades involved in the house only two, the roofers and the stucco people met or exceeded expectations. There's a long list of shoddy workmanship. There were many labourers that said they were tradesman, because they had done the same thing on 10 houses.
Everyone claimed they knew what they were doing, but, they didn't.
On our previous house, the water heater failed during a cold snap. We couldn't get a plumber. I went to HD, bought a tank came home and waited. 2 days later I installed it. A plumber finally said he would come and I wanted him to check my work. He said I did a great GJ job and looked up and said, 'that's not right', and poked the chimney on the furnace. The chimney fell apart. Turns out the guy had just friction fit the chimney and never put in the screws. The house had no inspection, although it should have.
Coming back to the thread topic, there are so many 'experts' on GJ, yet nobody says they are a licensed or journeyman tradesperson. If the lack of inspections is true any bumpkin can run around doing work. Here we have strong trade education and certification, licensing and inspection.
I am amazed at the stuff that the home inspectors post on TikTok. If you want to see a ton of incompetence look at "ChimpContracting", he's a completion inspector on commercial projects. They are large commercial projects and it amazing that people do things they know are wrong.
So to summarize, you got a gas heater, read up on the internet, then did the install, didn't get it inspected., then asked if it was alright to a bunch of unknown self proclaimed experts.