What causes heater short cycling and how can it be fixed?

One of the most common heating repair calls our team receives is for heater short cycling. Essentially, this is where a furnace, heat pump, or ductless system is constantly starting and stopping operation. In most cases, this not only wastes energy, but also puts additional strain on the system itself.

In this article, we’ll review what short cycling is, why it matters, what the common causes of this problem are, and what you should do to address this issue if you suspect your system is experiencing this fault.

A technician looks inside a furnace experiencing heater short cycling issues.What is heater short cycling?

In the HVAC world, a “cycle” is the period of time a system runs before shutting itself off. Cooling and heating systems running normal cycles will run until the temperature in the home has been sufficiently altered. Under normal conditions, a furnace or heat pump will cycle several times per-hour, turning back on when the temperature inside the home begins to drop again.

“Short cycling,” as can be inferred from the name, is a malfunction where the system runtimes are very short, leading the system to turn itself on and off very frequently. When short cycling, the system rarely runs for more than a few minutes at a time. If you listen for the sound of the system turning off and on again, you’ll probably hear it more than a dozen times in an hour. This is a potential sign of a short cycling system.

Does short cycling matter?

Yes. Short cycling is problematic. It may be an indicator that something is wrong with your heating system. A short-cycling unit is wasting more energy than it needs to and experiences far greater wear-and-tear than a comparable system that is running normally. In situations where your furnace, heat pump, or ductless system is running incredibly short cycles, you should bring in an experienced HVAC technician to diagnose the issue.

What causes short cycling?

The three most likely causes of furnace or heat pump cycling are improper sizing, thermostat issues, and poor insulation. Here’s what you should know about all three:

Improper sizing and installation

Most people automatically assume that, when it comes to HVAC systems, bigger is better. After all, who wouldn’t want more heating in their home? When taken at face value, it’s easy to see why most homeowners think that a furnace or heat pump with a higher capacity will heat their home more effectively and quickly.

However, it doesn’t work like that. In fact, a system that is too large for your home can lead to a number of performance and efficiency problems, including short cycling.

All heating and cooling systems are at their most efficient when running normally, maintaining the temperature of the home instead of having to significantly change it. A system that is too large for your home has trouble doing this. It will start up, run, and quickly raise the indoor temperature. Then, it will shut off: it is incapable of keeping your home’s temperature in that “sweet spot” without wildly overshooting what’s on the thermostat. The indoor temperature then drops again, and this cycle repeats. The larger furnace needs to run many, many short cycles within the hour to maintain the temperature, leading to significant energy waste.

By the way, a system that is too small for your home will often experience the opposite problem: no matter how hard it works, it will struggle to maintain the temperature of your home. This is also far from ideal, and it’s why you always want a professional HVAC technician to measure your home prior to selecting a system and having it installed.

Thermostat issues

A faulty thermostat can also be responsible for short cycling problems. The thermostat provides your furnace or heat pump with instructions about when to run, based on what the indoor temperature is. However, faulty wiring within the thermostat can often lead to poor instructions being sent to the system, which results in the heater clicking on and off repeatedly without consistently running.

If you suspect that your thermostat might be the cause of your short cycling issues, you’ll want to have a certified HVAC specialist out to your home to inspect the thermostat and its wiring. If it’s not the thermostat, the technician can at least rule it out and move on to investigate other potential issues. If it is the thermostat, it might need to be replaced with either a similar model or a new programmable thermostat.

Poor insulation and airflow

Next, try cleaning the air filter that leads to your furnace. A clogged air filter has the potential to choke off the airflow to the system, leading to a number of performance problems—including cycling issues.

Poor insulation is another potential problem that you should investigate with the help of your HVAC technician. Your heating system is more likely to cycle if your home has poor attic or wall insulation, you have major air leaks in your home, or your ducts are leaky. All homes lose some degree of their generated heat, but homes that are poorly insulated are losing this heated air so quickly that the furnace is constantly caught in the bind of having to catch up.

What is the best way to deal with this issue?

Call us today have a certified technician from our team come to your home. We offer heating repair here in Fresno and the Central Valley. At Allbritten, our experienced, friendly technicians fix all heating systems, makes, and models. We’ll diagnose the issue with your heater and get it back to heating your home efficiently and effectively.