Why Does My Furnace Keep Turning On And Off

Why Does My Furnace Keep Turning On and Off? Troubleshooting Short Cycling

A furnace that constantly cycles on and off, a problem known as "short cycling," is more than just annoying – it's a sign of potential trouble. This frequent on-off pattern wastes energy, reduces efficiency, and could lead to premature furnace failure. This article will explore the common causes of this frustrating issue, helping you diagnose and potentially fix the problem before calling a professional.

Understanding Short Cycling: More Than Just An Annoyance

Short cycling is defined as your furnace turning on and off repeatedly within a short period, typically less than 15 minutes. Instead of running consistently to maintain a set temperature, it experiences these rapid cycles, impacting your comfort and energy bill. The constant on/off action places added stress on the system's components, leading to potential breakdowns and costly repairs down the line. Ignoring short cycling can significantly reduce the lifespan of your furnace.

Common Causes of Furnace Short Cycling:

Here are some of the most frequent culprits behind a short-cycling furnace:

• Dirty Air Filter: A clogged air filter restricts airflow, causing the furnace to overheat and shut down prematurely as a safety measure. This is the easiest and most common fix. Check and replace your filter regularly (ideally every 1-3 months, depending on usage and filter type).

• Frozen Evaporator Coil (Heat Pumps Only): If you have a heat pump, ice buildup on the evaporator coil can restrict airflow and cause the system to short cycle. This often occurs in cold, humid climates. Allowing the system to thaw out completely, or if persistent, calling for professional help is necessary.

• Faulty Flame Sensor: The flame sensor detects the presence of a flame. If it's dirty or malfunctioning, the furnace might repeatedly shut down, believing the flame isn't ignited correctly. This requires cleaning or replacement.

• Faulty Limit Switch: Limit switches are safety devices that prevent overheating. If a limit switch is malfunctioning, it may prematurely shut off the furnace even when it's not overheating. This usually necessitates professional repair or replacement.

• Problems with the Blower Motor: A malfunctioning blower motor can impact airflow and cause the furnace to short cycle. This could involve issues with the motor itself, the capacitor, or the motor speed.

• Improperly Calibrated Thermostat: An inaccurate thermostat can cause the furnace to cycle on and off too frequently. Check the thermostat's batteries, ensure accurate calibration, and consider a professional calibration if needed.

• Refrigerant Leaks (Heat Pumps Only): Low refrigerant levels in a heat pump can cause it to short cycle. This is a more serious issue and requires professional attention for safe refrigerant recharge.

Troubleshooting Steps:

Before calling a technician, try these basic troubleshooting steps:

1. Check the Air Filter: This is the first and most important step. A dirty filter is the most common cause of short cycling.

2. Inspect for Obstructions: Ensure there are no obstructions blocking airflow to or from the furnace, such as furniture or debris.

3. Examine the Thermostat: Check the batteries, verify the thermostat is set correctly, and ensure it's not malfunctioning.

4. Listen for Unusual Noises: Any unusual banging, rattling, or clicking sounds could indicate a mechanical problem requiring professional attention.

When to Call a Professional:

If you've checked the simple solutions and your furnace continues to short cycle, it's time to call a qualified HVAC technician. They possess the expertise and tools to diagnose more complex problems such as faulty components or refrigerant leaks. Ignoring a persistent short cycling problem can lead to further damage and increased repair costs in the long run. Don't hesitate to seek professional help to ensure the safety and longevity of your heating system.

By understanding the common causes and taking proactive steps, you can address your furnace's short cycling issues and keep your home warm and comfortable throughout the colder months.