Most homeowners are familiar with a heater or home furnace being on a cycle. It involves the startup or warm-up process triggered by a temperature sensor, the burn phase, the hot air blowing, and then the furnace powering down and cooling when the target temperature in the home is reached per the same sensors. However, when a furnace malfunctions, it may start “short-cycling.” What causes furnace short-cycling occurs when the furnace basically shuts off before the home ever reaches its target warmth temperature.
How a Normal Cycle Should Occur
The normal turn-off process basically cuts off the burn activity so that the furnace can cool down. Air still moves through the system, which helps with the cooling off and captures the last of the heat before the furnace is sufficiently cooled. However, when the furnace continues to cut off too early, and this behavior continues repeatedly without proper heating occurring, then there is a malfunction that needs to be checked and repaired. The problem becomes noticeable, especially in cold months with the furnace turning on repeatedly and quickly because the house keeps getting cold again, reaching its trigger point. Some furnaces have been as bad as almost eight short cycles in an hour’s time.
Safety Features and Cut-Offs
Most modern furnaces and heating systems for homes have safety features for preventing fires and protecting the home. These protections can also be the source of many short-cycle situations, especially if the safety feature is malfunctioning. That can happen with a bad sensor, something causing the sensor to trip, or a failing part elsewhere in the furnace causing it to behave out of an acceptable heat range for the phase it is in.
Other safety sensors can trigger shut-offs as well. Carbon monoxide leak sensors may be triggered by a failing part or break in the furnace containment that allows the gas to escape. CO is highly dangerous, both because it can kill quickly and the fact that it has no color or smell. The CO gas when inhaled starves the body of oxygen, causing victims to pass out and then suffer brain damage or death from oxygen starvation. It’s a very serious risk that, unfortunately, comes with anything that burns like a furnace. So, safety features are installed to prevent leakage aside from normal venting.
Equipment Failures
Other triggers can include the flame igniter not working properly as well as a malfunctioning thermostat. Clogged air filters will also join the list of equipment failures. Air filters are essential for clean operation, and a clogged dirty one will create significant air pressure, forcing the furnace blower to work harder. Sensors will pick up this strain and shut off the furnace to avoid overheating. The same goes for blocked flue, which allows exhaust to escape outside.
Repair and Service
If there is clearly a short-cyling pattern in play, homeowners shouldn’t try to guess their way in trying to fix the problem. Absent changing the filter not solving the problem, there is going to be very little one can do with basic tools. In these situations, a full review is needed by a professional furnace or HVAC technician trained in dealing with short-cycling problems. The symptom is frequently a sign of a failing part, system or obstruction. So, the fact that the furnace keeps shutting off may very well mean something bigger needs to be fixed versus just a sensor tripping.
A professional HVAC or furnace team is going to know how to deal with short-cycling in different furnace models. It’s a safer approach, and the diagnosis will be provided accurately based on what’s actually happening versus uneducated guessing. Remember, a furnace deals with fuel or natural gas, so it needs to operate safely. Don’t risk your home safety to a do-it-yourself attempt. Bring in a professional team for the fix.
