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Why Does My Furnace Make a “Boom” Sound When It Starts Up?

If you own a gas furnace, it’s highly important to keep an eye and an ear out for any unusual behavior it might be exhibiting, especially if you haven’t used the equipment for an extended period. While it’s normal to hear your furnace whenever it turns on and runs, if it makes a boom, bang, or popping sound when it starts up, the equipment should be inspected by a professional HVAC technician.

Below, we’ll explain what causes the “boom” you hear and why it’s a problem that needs to get checked out as soon as possible.

Why Is My Gas Furnace Booming and Banging?

Delayed ignition is the reason why your gas furnace booms, bangs, or pops whenever the equipment starts up. But what is delayed ignition, and how does it happen? The short answer is that something is preventing the gas in your furnace from igniting (lighting up) right away.

When your furnace is working correctly, the thermostat will trigger it to turn on. At that point, the gas valves will open and release flammable gas for the burners, and the gas will ignite right away. When delayed ignition occurs, the released gas just keeps accumulating because, for whatever reason, it won’t ignite.

The gas will continue to collect inside the furnace until it finally makes contact with a flame. When that happens, the gas ignites in a small explosion, creating a pop, boom, or bang that you can hear.

Is Delayed Ignition a Safety Hazard?

While it’s not incredibly likely that your whole house will explode, delayed ignition can lead to equipment issues and safety hazards. Every time an explosion goes off in your furnace (even a small one), the impact of it puts stress on the machinery. Eventually, your furnace’s heat exchanger can crack, and this is one of the most costly heating repairs to perform. What’s more, a cracked heat exchanger can start leaking carbon monoxide and other poisonous fumes into your indoor air.

Delayed ignition can create another hazard: excess flammable gas. If you own an older furnace and attempt to reignite your pilot light, excess gas in the equipment can cause a flash fire, which can give you severe burns.

Does Delayed Ignition Require a Repair?

Unfortunately, delayed ignition is a problem that will not get better with time or fix itself. Furthermore, its exact cause can be difficult to diagnose without professional training.

These tend to be the most common reasons why furnaces have issues with delayed ignition:

  • The burners are clogged with dirt and dust. This typically happens when a furnace never or rarely has preventative maintenance.
  • The burners have become misaligned. An HVAC technician can realign them safely and relatively easily.
  • There is an incorrect natural gas to air ratio in the gas mixture being supplied to the burners. If there is too much air or too little air, the gas mixture can take longer to light up.
  • The furnace’s firebox has corroded. When not in use for long stretches of time, your furnace can collect moisture. This can cause corrosion to occur in the furnace’s firebox. The corrosion product that builds up can start to prevent gas from reaching the burners.

Most of these issues can be avoided by scheduling routine maintenance for your furnace once a year. Experts recommend completing that maintenance in the fall, right before your heating system is about to go through intensive use. This gives you a chance to ensure that the equipment is ready to operate safely and efficiently before you’re relying on it heavily.

At Meyers Companies, Inc., our technicians have the training and experience to get to the bottom of your home’s heating issues. For heater repair and maintenance in Griffith, don’t hesitate to contact us online or call us at (219) 240-0610.