What Causes My Heater To Short-Cycle?

When the winter temperatures dip, you need a reliable heating system to get your family safely through. Unfortunately, heaters do malfunction from time to time. One of the more common problems you may experience is your unit frequently turning on and off. This is known as short cycling and can indicate various problems with your system.

What Does It Mean When a Heater Is Short-Cycling?

When your system short-cycles, it will turn on and run for a short period of time. Then, it will turn off before it brings your home up to your desired temperature setting. This repeated on-and-off cycle can put a big strain on your heating system and make it more likely to fail. Additionally, the constant strain on your heater will shorten its overall lifespan.

Furnace short-cycling can prevent your home from being evenly warmed. You’ll experience a decrease in comfort and more frequent temperature swings. This frequent cycling is very inefficient and can cause a steady increase in your energy bills for the winter. If the short cycling is caused by something like a blocked vent or cracked heat exchanger, it could pose a major safety hazard. Having toxic fumes, like carbon monoxide, trapped inside your home can be exceedingly hazardous, even leading to fatality in severe cases.

When your heater doesn’t run through an entire cycle, it can’t provide adequate air filtration for your home. This can allow unwanted dust and allergens to build up. One thing to keep in mind when it comes to system short cycling is that it’s indicating an underlying problem with your unit. It’s best to get a professional evaluation from our team to get to the root cause of the issue. Ignoring short cycling could lead to bigger system problems over time.

What Is the Most Common Cause of Heater Short-Cycling?

The most common reason your heater may be short-cycling is due to restricted airflow. This happens when there’s a dirty air filter that’s limiting the movement of air in your ducting. When there isn’t adequate airflow, heat will build up inside your heating system. Your heater has an internal limit switch that will shut the furnace off whenever it senses that it’s overheating.

This is why your unit constantly shuts off before it adequately warms your home. If the airflow restriction isn’t caused by a dirty air filter, it may be due to restricted air vents and registers. If one or more of your vents or registers are closed or obstructed, it can restrict airflow. This will lead to overheating and the short-cycling that you may be experiencing. In some cases, the obstruction could be located inside your ducting. Examples include nesting from pests or major debris buildup from inadequate duct cleaning.

One cause that may not immediately come to mind is your thermostat. If the thermostat itself is faulty, has poor placement, or incorrect wiring, it could cause your short-cycling issue. For example, if your thermostat is placed in direct sunlight, it could falsely lead to a higher temperature reading. This can result in your unit shutting off suddenly before it truly goes through an entire cycle.

All modern-day heaters have safety sensors that are intended to prevent them from creating a fire hazard in your home. These are known as limit switches and will shut your system off in the event of overheating. Unfortunately, if your furnace’s limit switch is faulty, it could falsely trigger your unit to shut off when it isn’t overheating.

If your furnace burns natural gas or propane, it has a burner that’s responsible for the combustion process. Each furnace has a built-in flame sensor that’s responsible for detecting when there’s a stable flame. If there’s no flame on the burner, the sensor will shut off the fuel supply to prevent excess gas from backing up inside your unit. While this is great for safety, it can be a real pain when the flame sensor malfunctions. It could malfunction due to a dirty sensor or a faulty one.

All modern-day furnaces have control boards that are responsible for telling them how to operate. Issues like faulty relays, loose wiring, and control board malfunctions can all interrupt your system’s normal heating cycle. This can cause the unit to shut down unexpectedly before it gets through an entire heating cycle.

One other culprit of short cycling is a cracked heat exchanger. This component is responsible for housing the toxic exhaust fumes that your unit burns on their way out of your ventilation system. As the heat exchanger gets older, it will crack. These cracks can allow more heat to escape into your furnace, causing it to overheat and trigger its limit switch.

For your furnace to run properly, it needs a steady supply of fuel. Whenever there’s an obstruction in this fuel supply line, it can cause the flame on the burner to go out. Without adequate fuel, your heater will repeatedly try restarting.

If your furnace burns natural gas, propane, or heating oil, it has a vent pipe to get rid of toxic exhaust fumes. Unfortunately, these flue pipes can occasionally become blocked by snow, debris, and even bird nests. When these hot gases can’t escape your unit, the heat will back up inside your furnace and trigger the limit switch.

Another potential cause includes an oversized heating system. If you just recently had your HVAC unit replaced and are now having this issue, it’s likely your unit is too large for your space. It’s necessary to downsize to a smaller unit that can complete a full cycle before shutting off.

How Do You Fix Heater Short-Cycling?

When you first notice a short-cycling issue, it’s important to start with basic solutions. The easiest way will be to check your air filter. Pull it out of its housing and hold it up to a light. If you can’t see through the filter, it’s time for a replacement. It’s best to regularly check your air filter every month and replace it when needed. Always have a spare filter on hand so that you can do a replacement whenever necessary.

If the filter is still in good condition, consider checking your vents. Inspect each supply and return vent to see if it’s open and free from any obstructions. Items like rugs, furniture, and even curtains can block your air vents and disrupt their airflow. You want to aim for a good three feet of open space surrounding the vent for optimal airflow in or out.

When Should You Call a Professional for Heater Short-Cycling in Killeen?

If your air filter isn’t dirty and your vents and registers have adequate airflow, then it’s time to call Deane Electric & Air Conditioning for professional heating repair assistance. It’s never a good idea to attempt DIY heater repair, as doing so could void the warranty on your unit. Instead, opt for calling our professionals who can perform warranty repair work for you. Our team can thoroughly assess the root cause of the issue and even provide heater replacement whenever necessary.