Hi there, I live in fresno California, I'm trying to flush my tankless water heater, there's nothing wrong with it, just for maintenance purpose. My question is why the recess box on my water heater has a locked on it. I don't even have a key to open it. Does the city of fresno don't allow us to maintain our own water heaters?

Do you own this building? I have installed Rinni and do not recall a lockable box.