December 16, 2023
Furnace maintenance

There are several reasons your furnace frequently shuts off in the middle of a heating cycle before it reaches the desired temperature. Most of the issues that can cause this to happen will need the attention of an HVAC technician. Due to the dangerous aspects of these repairs and situations, it’s not advisable to attempt the fixes on your own. Let’s take a look at six reasons this issue could potentially be happening.

1. Overheating

Overheating is a common reason a furnace will shut off before it has reached the desired temperature. All modern furnaces have a furnace limit switch. The switch, which works in tandem with the blower to ensure the appliance is at a safe temperature, will turn off the burners if the temperature gets too hot, only letting them start again when it’s safe to do so.

If your furnace constantly overheats and frequently short cycles, the appliance may be too large for your home. An oversized furnace produces too much heat too quickly. This means that the heating system can’t disperse the heat fast enough, leading to the heat exchanger quickly getting too hot and the limit switch triggering a shutdown. Unfortunately, the only solution to this problem is to replace the furnace with a correctly sized unit.

Another common reason a furnace will overheat is that it doesn’t have enough airflow. This usually happens because the air filter is clogged to where very little air can go through it. If you suspect your furnace is overheating, the first thing to do is replace the air filter and see if this resolves the issue.

You also want to check that all supply and return vents are open and not blocked by furniture or any other bulky items. If the return vents are clogged or obstructed, almost no air will be drawn into the furnace, and it will quickly overheat. The air can’t get dispersed properly, causing it to build up inside the furnace to where the appliance overheats.

If the air filter is clean and all the vents are open, the issue likely means that the blower isn’t moving air through the system properly. An HVAC technician needs to come in and evaluate why the furnace is overheating and what they can do to fix it or if a replacement will be necessary.

2. Electrical Issues

Furnaces have several internal components and safety switches that use electricity to send signals to and receive signals from the control board. There is also a wire that runs from the thermostat to the furnace so that it can signal it to turn on and off. If any components have a loose or damaged electrical connection, they will sometimes randomly stop working and cause a shutdown.

Electrical issues can also easily lead to a fire, putting your residence, everyone in it, and even neighbors in danger. This is one of the many reasons annual furnace maintenance is so important. The technician will always check that all electrical connections are tight and none of the wiring is damaged and a potential fire risk.

3. Thermostat Issues

A furnace that frequently shuts down too soon can also be a sign that the thermostat isn’t working correctly and needs to be replaced, repaired or recalibrated. Older thermostats often have issues where they no longer correctly sense the temperature or they’re unable to correctly do so. This can lead to the thermostat signaling the furnace to shut off before it has reached the correct temperature. When troubleshooting your heating system, one of the first things the technician will do is test the thermostat to see if it’s working properly.

4. Malfunctioning Flame Sensor

The flame sensor is one of the most important safety components in a gas furnace. Its purpose is exactly what it sounds like. It senses via a rod that the flames from the burner are going strong, at which point it shoots off an electrical alert to the control board that all is going well and operating as expected. No flames means no alert, which triggers the furnace to shut down.

The flame sensor can also become coated with dirt and grime, which could cause it not to work properly. If it’s been a while since this component was cleaned, there’s a good chance it requires an expert to come in and clean it so that it operates properly once again. Considering the importance of this safety component, it’s one you certainly want to make sure is working at peak condition.

5. Exhaust Flue Isn’t Venting Properly

Most modern furnaces have a draft inducer fan that pulls the combustion fumes from the heat exchanger and into the exhaust flue. It’s one of the first things that turns on when the furnace does so that it has a chance to remove these fumes and get them out of your home. Its other important job is to ensure the burners have oxygen.

The air pressure switch is another essential safety mechanism that ensures that the fumes are being properly vented out through the flue. If the heat exchanger is partially blocked or the furnace isn’t venting as it should for any reason, the air pressure switch triggers the furnace to shut down. A furnace that isn’t venting properly is a major safety hazard since it can allow carbon monoxide to leak out into your home. Have a carbon monoxide detector installed near your furnace as a backup preventative safety measure.

6. Furnace Flame Rollout

Many newer furnaces have another incredibly significant safety feature called a flame rollout switch. Essentially, it indicates when there’s, as the name implies, a flame rollout, which is where the burner’s flames aren’t moving forward and going into the heat exchanger as normal. Instead, they go the opposite way where they’re certainly not supposed to be going, and they begin damaging your furnace in the process.

There are multiple reasons this switch may trip, including if a component, such as the heat exchanger, is clogged. If a flame rollout occurs, the switch will instantly shut off the burner’s gas supply. A flame rollout is also a serious safety hazard since it can easily start a fire. This issue can also cause major damage to your furnace as the flames can start to reach electrical wires and other components that aren’t designed to handle extreme heat. It’s vital to shut down your furnace, call an expert in right away, and don’t put the furnace back on until it’s checked out by a professional. You also don’t want to attempt to fix the issue yourself considering how dangerous it is.

With decades of experience serving customers in Greenville and the Fox Valley area, Black-Haak is the company to trust for all your heating needs. Our experienced, certified technicians can diagnose all furnace issues with professionalism and respect for you and your property. We service and repair all furnace makes and models and do replacements and installations. Our family-owned company also provides air conditioning, electrical and plumbing services. Call us today to schedule a furnace repair or any other heating services you need.

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