If you own a gas furnace, you have the benefit of enjoying a powerful heating system with a relatively low-cost fuel source. That being said, you should get the equipment professionally maintained and inspected once a year to avoid health and safety hazards.
Below, we’ll explain four potentially dangerous gas furnace issues.
A Faulty Thermocouple or Flame Sensor
If you own an older gas furnace with a standing pilot light, it has a thermocouple, whereas newer gas furnaces have a flame sensor instead. A thermocouple and flame sensor essentially have the same purpose: to prevent a dangerous buildup of gas in your furnace’s combustion chamber. A faulty thermocouple or flame sensor means that your furnace could accumulate a high concentration of flammable gas. If something were to ignite that gas, it could create an explosion.
If your furnace has a standing pilot light, the thermocouple’s tip should be positioned in the pilot light flame. That way, if the pilot light goes out, the thermocouple will detect the temperature difference and shut off the gas valve.
If your furnace operates via electronic ignition, it will either use:
- an intermittent pilot light that lights up only when your furnace is about to start heating;
- or hot surface ignition, which uses an electrical device that gets hot enough to ignite the gas to the furnace burners and then shuts off.
In these newer models, the flame sensor’s job is to make sure that the burners have ignited. If the sensor detects an ignition problem that has prevented the burners from lighting, it will shut off the gas supply.
Does your furnace make a boom or bang when it starts up? If so, then there’s a 99% chance that it has a delayed ignition issue. Delayed ignition occurs when the burners are getting gas, but something is preventing that gas from lighting up right away. Consequently, that gas has a chance to build up, and when it finally ignites, it’s creating a small explosion.
Delayed ignition is bad for a couple of reasons. For one, each time the gas bursts in an explosion, it puts stress on your furnace’s components and can cause them to break. Delayed ignition also creates a hazard. Because the problem allows your furnace to fill up with extra (flammable) gas, you could get burned by a flash fire if you try to manually relight the pilot light.
A Cracked Heat Exchanger
The air that warms up your home never actually comes into contact with your furnace flames. Instead, your furnace’s blower blows cold air from your home over a hot component called the heat exchanger, which transfers heat to the air and makes it warm. This allows your indoor air to heat up without being contaminated by pollution and flue gases that result from the combustion process.
As heat exchangers warm up and cool down repeatedly, their metal expands and contracts, and eventually, this can make the material brittle. Overheating from a lack of airflow can also stress the metal to the point of breaking. If your heat exchanger cracks, toxic flue gases will leak through and begin to infiltrate your breathing air.
An Incorrect Air-Fuel Ratio
Your gas furnace needs the correct mixture of natural gas and oxygen to burn efficiently and produce as little pollution as possible. If your furnace flame is blue, then you know that combustion is happening efficiently and safely. Sooty residue or a flame with yellow or orange streaks are telltale signs of incomplete combustion: in other words, your furnace is getting too little oxygen or too much gas.
Why is incomplete combustion a problem? From a monetary standpoint, it will waste gas and increase your energy bills. From a safety standpoint, incomplete combustion produces higher levels of carbon monoxide (CO). If this lethal gas were to leak into your air supply (through a cracked heaxzt exchanger, for instance), you and your family could be poisoned. Exposure to even low CO concentrations can result in long-term health damage, even after you remove the CO source.
Tips for Avoiding Dangerous Furnace Issues
- Get your furnace inspected and maintained by an HVAC professional once a year.
- Routinely clean or replace your air filter (depending on the type) to prevent airflow problems and overheating.
- Equip your home with carbon monoxide detectors.