If you are using a gas furnace, then a gas leak is one of the most serious problems you can ever face with your heating system. Below are some of the common causes of gas leaks.
Cracked Heat Exchanger
The heat exchanger is the part of the furnace that actually heats the air that eventually gets distributed to warm up the house. The heat exchanger comprises a series of metal tubes that burn fuel and get heated. Cool air passes over the tubes and gets heated in the process. This means the tubes can leak gas if they get damaged or cracked. This might happen, for example, if the heat exchanger gets overheated or succumbs to accumulated wear and tear after several years.
A cracked heat exchanger is dangerous for two main reasons. First, it can leak dangerous gases (such as carbon monoxide) into your home. Secondly, it can lead to further overheating, which might cause further damage to the furnace.
Gas Line Damage or Wear
In some cases, it is not the actual furnace, but the lines supplying it with fuel, that leak gas. For one, this might happen if the furnace is old and the seals on the gas connections are worn-out. It might also happen if something damages the gas lines and allows fuel to leak. Leaky furnace lines can lead to furnace inefficiency and furnace fires, so they are best handled by a professional as soon as possible.
In normal furnace operations, exhaust furnace gases should flow out of the furnace, up the flue, and into the atmosphere. In some cases, however, the exhaust gases flow back into the house instead of exiting the house. This might happen, for example, if the flue is clogged or if the house is so airtight that outside pressure is much higher than inside pressure. In such cases, even partially burnt gasses can also flow back into the house. The backflow can affect your household's health, so you need to fix it as soon as possible.
Improper Installation or Repair
Lastly, improper installation or repair of the furnace can also lead to gas leaks. The risk is especially high for DIY furnace owners. For example, you might fail to fix the gas lines correctly or forget to include a seal where it should be included, leading to gas leaks.
If you suspect a gas leak in your house, put out any naked flames (such as candles) in your house immediately. Don't operate any electrical or electronic devices or appliances (they might spark and cause an explosion). Turn off the gas supply, assuming the control is in an accessible location. Lastly, call your gas company and an emergency heating plumbing technician to help you diagnose and fix the cause of the leak.