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Furnace Troubleshooting: 10 Common Problems and How to Fix Them
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Oct 07, 2024 • 19 Min

Furnace Troubleshooting: 10 Common Problems and How to Fix Them

There’s nothing quite like a Seattle, Washington winter to remind you just how important a heating system is. But, as with all mechanical systems, your heater can act up when you least expect it. It’s happened to many homeowners I’ve worked with: one minute, the heater is humming along, keeping everyone cozy, and the next, it’s blowing cold air or, worse, nothing at all. So, let’s talk about some of the most common furnace issues I’ve encountered over my years in the field, how you might troubleshoot these problems, and when it’s time to call in a professional.

Pre-Troubleshooting Checks

Check Your Thermostat and Furnace Settings

Before we discuss troubleshooting furnace issues, it’s essential to ensure that your thermostat and furnace settings are correct. Here are some pre-troubleshooting checks to perform:

  • Thermostat Settings: Make sure your thermostat is set to “heat” mode and the temperature is high enough to trigger the furnace. It might sound simple, but I’ve seen many cases where the thermostat was accidentally set to “cool” or the temperature was too low to activate the furnace.
  • Thermostat Functionality: Check the display on your thermostat. If it’s blank or showing an error message, it could be a sign of dead batteries or a malfunctioning unit. Replace the batteries if needed and ensure the thermostat is functioning correctly.
  • Furnace Settings: Verify that your furnace is set to the correct mode, such as “heat” or “auto.” Sometimes, the settings can be accidentally changed, especially if you’ve recently had maintenance or repairs done.
  • Furnace Door: Ensure the furnace door is closed and secure. An open or improperly closed door can prevent the furnace from operating correctly. I once had a call where the furnace wouldn’t start simply because the door wasn’t latched properly after a filter change.

By performing these pre-troubleshooting checks, you can quickly identify and resolve any issues related to your thermostat or furnace settings, saving you time and potentially avoiding unnecessary repairs.

What Are the Most Common Furnace Problems?

1. The Heater Isn’t Turning On

Picture this: you’ve set your thermostat to heat, but nothing happens. It’s like when you text a friend and they don’t reply – frustrating, right? The first thing to check is whether the thermostat is set to “heat.” Believe it or not, this is a common oversight. I’ve shown up to plenty of homes only to find the thermostat was off or set incorrectly. If it’s set properly and still won’t activate, the issue could be electrical.

Furnace thermostat repair, photo by Ben's Plumbing

DIY Furnace Repair Tips:

Make sure the thermostat is set to the correct temperature and mode. Replace the batteries if it’s not hardwired, and double-check that the circuit breaker hasn’t tripped. If the system still won’t respond, it’s time to investigate further. This is when we start looking at more complex furnace troubleshoot efforts, like checking for blown fuses or faulty wiring.

In my experience, it’s not uncommon for homeowners to overlook simple fixes. One memorable job involved a family that had a perfectly functioning system but had accidentally turned off their circuit breaker during some home renovations. A quick flip of the switch, and they were back in business. Still, if you’ve gone through all the basics and still find your furnace not working, professional help may be needed.

2. The Heater Blows Cold Air

I’ve had homeowners panic when their system is on, but instead of warm air, it’s blowing an arctic chill. This could be caused by a few issues. In one instance, I found the problem was simply a dirty air filter, which had caused the system to overheat and shut off. A clogged furnace filter can also lead to inefficient heating by causing the furnace to short cycle, making it harder to maintain a consistent temperature in the home. Other times, the pilot light was out, especially in older gas units.

DIY Furnace Repair Tips:

Regularly replace your air filter—every 1-3 months is recommended, especially in cold weather seasons when the system is working overtime. If you’re dealing with a gas furnace problems, you’ll also want to check the pilot light. If it’s out, relight it following your manufacturer’s instructions, or call a pro if you’re uncomfortable doing it yourself. If that doesn’t fix it, the issue could be more serious, like a broken fan or a malfunctioning blower motor, requiring a professional fix.

I remember one call where a family couldn’t figure out why their heat wasn’t coming through properly. After inspecting their system, I found that their filter hadn’t been changed in nearly a year. It was so clogged that no air could pass through, causing the system to cycle cold air. Once we replaced the filter, everything was back to normal. If your heater is not working or the air is cool, check the simple fixes first.

3. The Heater Turns On and Off Frequently (Short Cycling)

I’ve walked into homes where the heater seems to have a mind of its own—turning on for a few minutes, then shutting down before it can properly warm the place up. This is called short cycling and can be caused by an oversized system, a clogged filter, or a malfunctioning thermostat. In one case, I diagnosed this issue in a home where the thermostat was too close to a heat source, causing it to shut off prematurely.

DIY Furnace Repair Tips:

Check for a dirty filter or make sure your thermostat is placed away from any direct heat sources. This includes things like lamps, ovens, or direct sunlight. Also, check the thermostat’s calibration—sometimes, recalibration can fix the issue. If the problem persists, you may need professional assistance to diagnose more complex issues like an improperly sized unit or issues with the limit switch, which can prevent overheating.

One homeowner I worked with had their thermostat located right next to a space heater in their living room. Every time they turned on the space heater, it would warm up the thermostat too quickly, causing the main system to shut down prematurely. Simply moving the thermostat to a more central location solved the problem. Short cycling is a common issue, but one that can lead to larger problems if left unresolved, so it’s something to address as soon as you notice it.

4. The Pilot Light Won’t Stay Lit

If your furnace stopped working, and you notice the pilot light keeps going out, it could be a thermocouple issue or a draft near the system. The flame sensor, a vital safety device, detects the presence of a flame to control the gas flow, and dirt accumulation can hinder its performance, leading to the furnace not working properly. I had one job where the homeowner couldn’t keep the pilot lit because their system was installed in a drafty garage, and the wind kept blowing it out.

DIY Furnace Repair Tips:

First, check if the pilot light is dirty or obstructed. Gently clean any debris that may be causing issues. Seeking professional help for gas furnace repair is crucial to ensure safety and proper handling. If the pilot light is still going out, it may be a sign that the thermocouple is faulty or that there’s a gas flow issue. I recommend leaving gas-related repairs to a professional, as they can be dangerous if not handled correctly.

In the drafty garage situation, we ended up installing a small shield to protect the pilot light from wind gusts, which solved the issue. But I’ve also seen cases where the thermocouple needed replacement, which is a fairly straightforward repair for a pro. If the furnace stops working due to pilot issues, don’t hesitate to get an expert involved, especially when dealing with gas systems.

5. The Heater Is Making Strange Noises

A heater can make a variety of noises when it’s in trouble—banging, squealing, or rattling. These sounds can be unsettling, but they often point to mechanical issues like loose belts or worn-out parts. I recall one case where the banging sound was caused by air ducts expanding and contracting due to poor insulation.

DIY Furnace Repair Tips:

If you hear a banging or rattling noise, turn off the system and check for any loose parts or debris in the blower motor. It might be something as simple as tightening a few screws. For squealing noises, it’s often a worn-out belt that needs replacement. If the noises persist after basic fixes, bringing in a professional is best to avoid further damage.

I’ve had calls where the homeowners were so worried about the noise that they’d shut off their heat altogether, only to realize it was a minor issue. In one case, the noise was a small screw that had come loose in the blower housing—an easy fix, but a noisy one if left alone.

6. The System Is Overheating

Overheating is a common cause of furnace problems, particularly when the system works extra hard during cold weather. Regular furnace maintenance is crucial in preventing overheating and ensuring efficient operation. An overheated unit can lead to shutdowns or even damage. Often, the root cause is a dirty air filter or blocked airflow, which forces the system to run hotter than it should.

DIY Furnace Repair Tips:

Replace your air filters regularly and ensure furniture or curtains don’t block your vents. If the system continues to overheat, it may be a sign that the blower motor or another component is struggling and needs professional attention.

7. Weak Airflow

If you notice weak or uneven airflow from your vents, it could be a sign of a problem in your ductwork or a clogged filter. I’ve seen homes where certain rooms are always colder than others, and it turns out the ducts were either poorly designed or blocked by debris.

Clogged ductwork, photo by Ben's Plumbing

DIY Troubleshooting Tip:

Check your air filter and replace it if it’s dirty. Also, inspect the ductwork where possible to ensure there aren’t any obstructions. A professional can also assess whether your ducts are properly sealed and sized for your home. Weak airflow can sometimes be fixed with a simple duct cleaning or repair.

8. Thermostat Issues

A malfunctioning thermostat can cause a wide range of common furnace issues, from short cycling to not turning on at all. Sometimes the problem is as simple as dead batteries or incorrect settings, but it can also be a sign of a failing thermostat that needs replacement.

DIY Troubleshooting Tip:

Replace the batteries in your thermostat if it’s not hardwired, and make sure it’s set to the correct temperature. If you’ve already done that and it’s still acting up, consider upgrading to a programmable thermostat or getting a professional to inspect it.

In one memorable job, I found that the homeowner’s thermostat had simply been knocked off the wall by their dog, causing it to disconnect from the wiring. It was an easy fix, but it’s a good reminder that sometimes the issue isn’t with the system itself but with the controls.

9. Dirty or Clogged Burners

Burners can get dirty over time, leading to inefficient operation and potentially causing the system to shut down. This is more common with older gas systems, where dirt and debris can accumulate on the burners, reducing their ability to produce heat.

DIY Troubleshooting Tip:

Cleaning the burners requires turning off the gas supply and carefully removing the dirt with a brush. If you’re not comfortable doing this, a professional can handle it safely during a routine maintenance visit.

I’ve come across homes where the burners were so clogged that the system was barely producing any heat. After a thorough cleaning, the unit was back to working efficiently.

10. The Blower Motor Isn’t Working

If you find that your system turns on, but no air is blowing through the vents, the issue may lie with the blower motor. This component is responsible for pushing air through the ducts and into your home. If the motor isn’t working properly, you’ll either get no airflow or weak airflow, which can make the system virtually useless.

DIY Troubleshooting Tip:

Before assuming the motor is broken, check to make sure the motor’s power supply hasn’t been disrupted by a tripped breaker. If the motor is still not running, it may be due to mechanical wear and tear or electrical problems. At this point, it’s best to call in a professional.

In one home I worked on, the family hadn’t noticed the decline in their blower motor’s efficiency until one particularly cold night when the house just wouldn’t warm up. Upon inspection, I found that the motor’s bearings were worn out, preventing it from operating at full capacity. We replaced the motor, and the house warmed up in no time.

Safety and Maintenance

Safety Precautions and Maintenance Tasks

Regular maintenance is crucial to ensure your furnace is working safely and efficiently. Here are some safety precautions and maintenance tasks to perform:

  • Power Off: Always turn off the power to your furnace before performing any maintenance tasks. This simple step can prevent accidents and ensure your safety.
  • Carbon Monoxide Prevention: Ensure that your furnace is properly installed and maintained to prevent carbon monoxide poisoning. Install carbon monoxide detectors in your home and test them regularly.
  • Filter Replacement: Check your furnace filter regularly and replace it every 1-3 months, depending on usage. A clogged filter can cause the system to overheat and reduce airflow, leading to various furnace problems.
  • Electrical Connections: Inspect your furnace’s electrical connections and wiring to ensure they’re secure and not damaged. Loose or frayed wires can cause malfunctions or even fires.
  • Visual Inspection: Perform a visual inspection of your furnace’s components, such as the heat exchanger, burner, and blower motor, to ensure they’re in good condition. Look for signs of wear, rust, or damage.

By following these safety precautions and maintenance tasks, you can help ensure your furnace is working safely and efficiently, and prevent common furnace problems from occurring. Regular maintenance not only extends the lifespan of your furnace but also keeps your home warm and comfortable during the cold months.

When to Call a Professional

While there are many basic troubleshooting tips that homeowners can tackle themselves, certain issues are best left to a professional for furnace repair. If you’ve tried everything and still have a heater not working, it’s time to pick up the phone and call an expert. Here are a few specific situations when professional help is necessary:

  • Repeated failures to start: If you’ve checked the thermostat, breaker, and power supply but the system refuses to start, the issue may be more complex, such as a problem with the control board or the internal wiring.
  • Frequent short cycling: If your system turns on and off too frequently, it could be an issue with the heat exchanger, which requires specialized knowledge to repair or replace.
  • Pilot light won’t stay lit: If relighting the pilot doesn’t solve the issue, the problem may lie deeper within the system, such as a faulty gas valve or thermocouple. Handling gas systems without the proper expertise can be dangerous, so always consult a professional in this case.
  • Gas smells or leaks: This is a serious safety issue. If you smell gas, shut off your system immediately, evacuate the house, and call a professional (or the gas company) to inspect your system. Never attempt to fix gas leaks on your own.

Over the years, I’ve worked on hundreds of systems where the homeowners tried to handle things themselves, only to make the problem worse. In one memorable case, a homeowner had attempted to clean their gas burners but ended up damaging the gas valve in the process, turning a minor issue into a much more expensive repair. It’s always a good idea to assess your own comfort level with DIY fixes and call a professional when in doubt.

Furnace Preventative Maintenance Tips

Regular maintenance can go a long way in preventing many common problems with furnaces. Recognizing symptoms and performing regular maintenance is crucial to avoid major furnace repairs.

Changing air filter, photo by Ben's Plumbing

Here are a few tips that can help keep your system in good working order and extend its lifespan:

  1. Change the Air Filter Regularly: One of the simplest yet most effective ways to prevent issues is by changing your air filter regularly. A clogged filter can cause the system to overheat, reduce airflow, and make the entire system work harder than necessary. I recommend checking the filter every month during the winter and replacing it at least every 1-3 months.
  2. Schedule Annual Tune-Ups: Just like your car needs an oil change and regular inspections, your heating system benefits from a yearly tune-up. A professional technician can inspect and clean the system, check for potential issues, and make any necessary repairs before they become bigger problems.
  3. Keep Vents and Ducts Clean: Ensure that all vents are open and unobstructed by furniture or curtains. Regularly cleaning your ducts can also help improve airflow and reduce the strain on your system. Dirty or clogged ducts can lead to inefficiency and higher energy bills.
  4. Inspect the Pilot Light: If you have an older gas system, it’s a good idea to check the pilot light periodically. A weak or flickering flame can indicate an issue that needs attention. The flame should be steady and blue—if it’s yellow or weak, it may be time to call a professional.
  5. Listen for Unusual Noises: Unusual noises are often the first sign of trouble. If you hear banging, squealing, or rattling, don’t ignore it. Investigate the source of the noise and take action before it turns into a bigger, more expensive problem.
  6. Monitor Energy Bills: If you notice a sudden spike in your energy bills without a corresponding increase in usage, it could be a sign that your system is working harder than it should. High energy bills are often the result of a system that needs maintenance or repair.

Common furnace issues conclusion

When your furnace stops working, it’s easy to panic, especially in the middle of winter. But by understanding some of the most common furnace issues and knowing how to handle basic troubleshooting, you can often resolve minor problems on your own. However, for more serious issues or anything involving gas or electricity, it’s always safer to call in a professional.

In my years of experience serving homeowners in the Greater Seattle and Eastside areas, I’ve seen it all—from simple fixes to major overhauls. If you’re experiencing heating issues, don’t hesitate to reach out for professional advice. Your home’s heating system is critical for keeping your family safe and comfortable, so stay on top of maintenance and address problems early before they turn into larger, more expensive repairs.

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By following the advice in this post, you’ll be well on your way to understanding how to fix a furnace and keeping your home warm during those cold Washington winters. If you need help, Ben’s Plumbing has been a trusted partner for over 25 years. Our team is not only licensed by the Washington State Department of Labor and Industries but also holds an AAA rating with the Better Business Bureau, thanks to their commitment to quality work and customer satisfaction. Plus, because their plumbers don’t work on commission, you can trust that they’ll only recommend what’s truly necessary to get your home’s heating system back up and running.

Frequently Asked Questions

What is the most common problem with furnaces?

The most common issue I see is dirty or clogged filters. These can cause your system to overheat, blow cold air, or shut down altogether. Regular filter changes are one of the easiest ways to avoid these common furnace issues.

How do you diagnose a furnace problem?

Start by checking the thermostat, power supply, and air filter. If those are working properly, the next step is to inspect the pilot light (if applicable) and listen for any unusual noises. If your DIY efforts don’t resolve the issue, it’s time to call a professional for a more in-depth inspection. A great option for homeowners in the Greater Seattle area is to reach out to Ben’s Plumbing, a family-owned company with over 25 years of experience. They’ve earned a reputation for being reliable and knowledgeable, and their team doesn’t work on commission, so they’ll never try to upsell you on a service you don’t need.

Why won’t my furnace heat up?

This could be due to a variety of issues, including a dirty filter, a malfunctioning thermostat, or a problem with the pilot light. Start by checking these components, and if the system still won’t heat, call in a professional for further diagnosis. If you’re looking for someone trustworthy, Ben’s Plumbing has a reputation for quality and professionalism, with a commitment to getting the job done right without unnecessary extras.

How can I maintain my furnace?

Regular maintenance is key to keeping your system in top shape. Change the air filter regularly, schedule annual professional tune-ups, and keep your ducts and vents clean. Also, listen for any unusual noises and address them promptly. Scheduling a tune-up with an experienced, licensed contractor like Ben’s Plumbing ensures that your system is running efficiently and prevents bigger issues down the line.

Ben Foster
Ben Foster
Owner
"The goal at Ben’s Plumbing is, and will always remain, to provide courteous, professional, personalized service to every home and business owner who puts their trust and confidence in Ben’s Plumbing."
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"The goal at Ben’s Plumbing is, and will always remain, to provide courteous, professional, personalized service to every home and business owner who puts their trust and confidence in Ben’s Plumbing."
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