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4 Potentially Dangerous Gas Furnace Issues You Should Never Neglect

With proper care and maintenance, you can expect to get a good 15-20 years out of your gas furnace. That being said, the occasional issue might still crop up, and some pose a more serious safety threat than others.


Below, we’ll explain which furnace problems call for a repair ASAP and what makes these issues potentially dangerous to your health or safety.

A Boom When Your Furnace Starts Up

If you hear a bang or a boom whenever your furnace starts to run, this means that your furnace has a problem called delayed ignition. For whatever reason, even though your furnace is getting gas, the burners aren’t immediately igniting. This causes the gas to build up inside the furnace’s combustion chamber, and when it eventually lights, it bursts in a mini-explosion.

These explosions put stress on your furnace and can lead to parts breaking down prematurely. A buildup of flammable gas is also dangerous, particularly if you own an old furnace with a standing pilot light. If you were to attempt to relight the pilot light by hand with excess gas still in the chamber, you could get injured by a flash fire.

Problems with the Flame Sensor (Thermocouple in Older Furnaces)

After reading about delayed ignition (above) you might be wondering what’s to stop your furnace from filling up with enough gas to make your whole home explode. The key is a safety feature called the flame sensor. If the flame sensor detects that the burners aren’t igniting, it shuts off the gas to your furnace. Similarly, in older furnaces, if the thermocouple can’t detect the standing pilot light flame, it will cut off the furnace’s gas supply.

With that in mind, you might see now how a faulty flame sensor could be an annoying problem and, at the worst, a very dangerous one. A faulty flame sensor can prevent your furnace from igniting by prematurely shutting off the gas supply, leaving you out in the cold. However, if the flame sensor doesn’t shut off the gas when it should, then you’ll have a furnace full of volatile gas.

An Incorrect Gas-to-Air Ratio

Your furnace doesn’t actually burn pure natural gas. It uses a natural gas and oxygen mixture. The proportions of the mixture need to be just right to ensure that the fuel burns cleanly–the less pollution the better. When the ratio of oxygen to gas is off, your furnace will create more pollution as it burns fuel. You may notice soot in your furnace and yellow or orange flames, as opposed to bright blue ones. This issue can also cause delayed ignition (explained above), which can cause a small explosion to occur inside your furnace whenever it starts up.

There are other effects of an incorrect gas-to-air ratio that are harder to detect right off the bat. For one, the issue makes your furnace less efficient, so you could see it take a toll on your heating costs over time. More importantly, your furnace will create more carbon monoxide as a byproduct of combustion. If your furnace is sealed properly, this deadly, odorless gas will be vented outside your home, but unfortunately for some homeowners, that is not always the case, which we’ll explain more below.

A Crack in the Heat Exchanger

Because your furnace burns fuels to produce heat, it creates some byproducts that are harmful to breathe. To keep you safe, that combustion process is kept sealed and separated from the air that circulates through your home. The component that stands in the “middle” is the heat exchanger. The combustion process heats up the heat exchanger on “one side,” and your breathing air blows over the “other side” of the heat exchanger. This allows the heat exchanger to transfer its warmth to your breathing air without allowing it to mix with soot, carbon monoxide, or other toxic combustion byproducts and flue gases.

The problem is that sometimes heat exchangers crack due to corrosion or stress from overheating (typically because the air filter hasn’t been changed soon or often enough). A crack that’s big enough allows toxic flue gases from your furnace’s combustion chamber to mix with your breathing air. Even if the concentration of these gases isn’t deadly, keep in mind that low concentrations to gases like carbon monoxide can still have enduring negative health effects, including “learning and memory impairments, emotional and personality effects, and sensory and motor disorders,” according to the EPA.


What’s troublesome about some of the issues is that they’re not easy to detect without professional training and equipment. As a homeowner, the best way you can safeguard your home is by routinely changing the air filter to prevent overheating, installing carbon monoxide detectors in all the recommended locations in your home, and getting your heating system serviced and inspected by a professional once a year.

For thorough, reliable heating services in Kingston, put your trust in JSP Home Services: (845) 209-1700 .


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