The gas upstairs and downstairs is in charge, and one has been left unattended.

If the main gas pipeline upstairs and downstairs passes through a house that has never been inhabited, the following steps can be taken:

1. sticker notice: you can put a small note on your neighbor's door to inform them that you want to have a gas check and ask them to open the door for you at their convenience.

2. Contact the property: If the note can't solve the problem, you can contact the property company, explain the situation to them and ask them to help solve the problem.

3. Seek professional help: If the above two methods fail to solve the problem, you can seek the help of professional gas pipeline testing companies, who can provide more detailed and professional testing and solutions.

Before doing anything, please make sure that you understand the relevant safety regulations and operating procedures. If you have any questions about the safety of gas pipelines, please contact local gas companies or professionals for help immediately.