Why Does My Gas Furnace Keep Starting and Stopping?
A gas furnace that keeps starting and stopping, also known as “short cycling,” can be a frustrating and potentially costly issue. This problem can be caused by various factors, including issues with the thermostat, airflow, or the furnace’s internal components. Understanding the underlying causes and following a step-by-step troubleshooting process can help you identify and resolve the problem.
What Causes a Gas Furnace to Keep Turning On and Off?
1. Is the Thermostat Functioning Properly?
The thermostat plays a crucial role in the furnace’s operation, as it signals the furnace to start and stop based on the desired temperature. If the thermostat is malfunctioning or not properly placed, it can cause the furnace to short cycle.
2. Is the Air Filter Dirty or Clogged?
A dirty or clogged air filter can restrict airflow, causing the furnace to overheat and shut down. Regularly replacing the air filter is essential for maintaining proper airflow and preventing this issue.
3. Are the Vents Blocked or Closed?
Blocked or closed vents can also lead to reduced airflow, causing the furnace to short cycle. Ensure that all vents are open and unobstructed.
4. Is the Flame Sensor Dirty or Malfunctioning?
The flame sensor is responsible for detecting the presence of a flame in the furnace. If it’s dirty or not functioning correctly, it can cause the furnace to shut off prematurely.
5. Is the Blower Motor Working Properly?
A faulty blower motor can fail to circulate air effectively, leading to overheating and the furnace shutting down.
6. Are There Issues with the Pressure Switch or Draft Inducer Fan?
The pressure switch and draft inducer fan work together to ensure proper airflow and exhaust. If either of these components is malfunctioning, it can cause the furnace to short cycle.
7. Is the Control Board Defective?
The control board is the “brain” of the furnace, responsible for coordinating the various components. If the control board is faulty, it can lead to the furnace starting and stopping repeatedly.
How to Troubleshoot and Fix a Gas Furnace That Keeps Starting and Stopping
- Check the Thermostat:
- Ensure the thermostat is set to “HEAT” and the temperature is set correctly.
- Verify the thermostat is located in a central, well-ventilated area, away from drafts or heat sources.
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Replace the thermostat batteries if necessary.
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Inspect and Replace the Air Filter:
- Turn off the furnace and replace the air filter if it is dirty or clogged.
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Clean or replace the filter every 1-3 months to maintain proper airflow.
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Ensure Vents are Open and Unobstructed:
- Check that all air vents are open and not blocked by furniture or other items.
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Clear any debris from the exhaust vent (flue pipe).
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Clean or Replace the Flame Sensor:
- Turn off the furnace at the breaker box.
- Locate the flame sensor, unscrew it, and clean it with a fine abrasive pad.
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If the flame sensor is still not working, replace it with a new one.
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Inspect the Blower Motor:
- Check for proper airflow by holding your hand near the vents.
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Listen for unusual sounds from the blower motor, such as buzzing, grinding, or screeching, which may indicate a faulty motor.
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Verify the Pressure Switch and Draft Inducer Fan Motor:
- Use a multimeter to check the pressure switch for continuity.
- Listen for the draft inducer fan motor and check for any unusual noises.
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Replace the pressure switch or draft inducer fan motor if necessary.
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Examine the Control Board:
- Inspect the control board for any visible signs of damage, such as burn marks or shorted components.
- If the control board appears to be faulty, replace it with a compatible model.
Remember to always turn off the furnace at the breaker box before performing any maintenance or repairs, and ensure proper ventilation to avoid carbon monoxide buildup.
Estimated Costs and Time Required for Repairs
The cost of repairing a gas furnace that keeps starting and stopping can vary depending on the specific issue and the parts required. Here’s a general estimate:
- Air Filter: $10-$30
- Flame Sensor: $20-$50
- Thermostat: $50-$200
- Blower Motor: $100-$300
- Pressure Switch: $20-$50
- Draft Inducer Fan Motor: $50-$150
- Control Board: $100-$300
The time required for these repairs can range from 15 minutes for simple tasks like checking the thermostat and air filter, to 1-3 hours for more complex repairs, such as replacing the blower motor, pressure switch, or control board.
Conclusion
A gas furnace that keeps starting and stopping can be a frustrating issue, but with the right troubleshooting steps and a bit of DIY know-how, you can often identify and resolve the problem. By checking the thermostat, air filter, vents, and key furnace components, you can pinpoint the root cause and take the necessary actions to restore your furnace to reliable operation.
Remember to always prioritize safety when working with gas furnaces, and consider seeking professional assistance if you’re not comfortable performing the repairs yourself. With the right approach, you can get your furnace back on track and enjoy consistent, comfortable heating in your home.
