1. Improper installation could lead to a gas leak.
This is absolutely the number one reason to avoid installing gas appliances yourself or performing a gas line pressure test yourself. It’s priority not only because your appliance won’t operate correctly (or possibly at all), but because it’s a serious health risk for you and your family members. In addition to being a serious fire hazard, inhaling gas fumes can be potentially fatal. This is an overall DIY no-no; call a professional!
2. Depending on the system you’re attempting to install, it could lead to damages to the system itself.
If the gas line isn’t properly connected or installed on an appliance such as a water heater, this will cause your water not to be heated. This one is kind of a no-brainer – if it isn’t installed correctly it won’t work correctly – that simple.
3. Improper installation can lead to damage to the surroundings of the system.
This one goes hand-in-hand with the previous point, because improper gas line installation can lead to other damages. In the same case of the water heater, this could lead to water leaks that will leave expensive damages in their wake. It’s much better to spend that money on having a professional install and test your system as opposed to “saving” money by doing it yourself but spending WAY more on repairs later on.