Furnace & Heater Troubleshooting Guide

By Kealia Reynolds

This guide will walk you through troubleshooting furnace and heating system problems and help you determine when to fix a common problem yourself and when to call on a professional.

Common furnace issues

These are the most common issues people experience with their heating system and the recommended course of action.

1. The furnace won’t turn on / no power

If your heater isn’t responding to the current temperature settings, there may be a tripped breaker, loose wiring, or a problem with your thermostat. Reset the circuit breaker and ensure the thermostat is set to heat with a temperature well above the current temperature of the room.

If your heater still doesn’t kick on, there could be a more severe problem with your furnace. The issue could be a faulty thermostat, control board, or blower motor. Call in a technician to run a diagnostic on your system and pinpoint the exact problem.

2. The heater runs but doesn’t produce heat

When this occurs, a clogged air filter could be blocking the air vents, preventing warm air from escaping. If your filter is dirty, clean it (if it’s reusable) or replace it (if it’s disposable). If your heater still isn’t producing warm air, make sure the thermostat is set to heat and the fan is set to on or auto.

If these steps don’t work, your blower may not be working properly or the unit may be out of balance—a problem that requires professional assistance.

3. The furnace cycles on and off too frequently

If your furnace is constantly cycling on and off, there may be a problem with the thermostat’s ability to detect the temperature of the room. Remove furniture or items too close to the thermostat. If this doesn’t fix the problem, check for dust or dirt behind the thermostat faceplate by removing the thermostat from the wall and using a cotton swab or Q-tip to clean any dirt, debris, or corrosion marks.

If you’re still experiencing issues, check the thermostat’s calibration. If your thermostat has a small lever that moves along a calibrated scale, try adjusting this—set it one calibration mark closer to the longer setting. It may take several hours for the thermostat to stabilize at this setting. You could also set a handheld thermometer next to the thermostat to see if there is a discrepancy between the two gauges.

If this doesn’t work, you might need a thermostat replacement—a professional can help you determine which thermostat is best for your heating and cooling systems.

4. There are strange sounds coming from the motor

Strange sounds, like squealing or whining, coming from your furnace or heater can mean a failing motor or a worn out belt. Though there are instructions in your heating system’s owner’s manual that tell you how to replace a failing motor belt, immediate attention from a technician is required to prevent a breakdown of your system. A professional can also handle the belt replacement safely and efficiently.

5. The burner isn’t igniting

If your furnace has a spark ignition, clicking sounds can indicate that a burner is trying unsuccessfully to ignite. The burner could have ignition problems due to a blocked flue, faulty control board, or improper limit control. A professional can determine which parts should be repaired or replaced to fix the problem.

6. The pilot light is faulty

If your furnace has a pilot light that won’t stay lit, the thermocouple—a copper rod that the pilot flame heats upmay be loose or the safety cutoff valve could be defective. In some cases, the pilot thermocouple needs to be adjusted or replaced. A professional can determine if this is necessary and complete the job.

7. The burner isn’t staying lit

A dirty flame sensor or clogged condensate drain could cause a burner to not stay lit. A technician can clean key components, ensure the gas supply line is on, and make a few adjustments to the system to ensure your burner functions properly.

8. The air filter is frequently clogged

A blower motor that runs all the time can cause an air filter to become clogged with dirt and other debris. This could restrict airflow, damaging the limit switch which senses the internal furnace temperature. A professional can replace the switch and make sure air is flowing properly again.

When should I call a professional?

If you’re stuck in the troubleshooting stage or are uncomfortable addressing a problem, always call in a professional.

Some repairs will require professional help if the issue is severe or a specific part is needed. In general, you should call a professional if:

  • The furnace won’t turn on
  • Your system regularly cycles on and off
  • The pilot light is out or has trouble igniting
  • Strange noises are coming from the system
  • You need to replace internal parts of the furnace
  • The blower runs constantly
  • The gas valves need to be replaced

Safety considerations

When repairing your heater or furnace, you could be dealing with heat, electrical wiring, or an open flame. Take extra precautions to prevent injurywear heavy-duty gloves and long, protective clothing. If you don’t feel that you can appropriately repair or tend to a repair, always call in a professional.

Furnace and heater maintenance tips

There are simple steps that you can take to avoid a costly furnace repair or replacement.

1. Schedule an annual furnace/heater inspection

Scheduling regular inspections for your system can reduce the amount of repairs in the future. During an inspection, a technician will check the safety features, thoroughly clean your system, and inspect key components of your system, like the burner, electrical connections, and thermostat, to reduce the chance of a system breakdown.

2. Change your air filter regularly

Your air filter will build up dirt, dust, and grime over time, reducing airflow and compromising the air quality in your home. Change your air filter every one to three months to improve the air quality and airflow throughout your home.

3. Address problems immediately

If a problem does arise, address it immediately. Paying for a service visit from a licensed professional could end up preventing major problems in the future.

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