The 10 Most Common Furnace Problems

Homeowners’ everywhere wonder, “What is wrong with my gas furnace?”  If you are one of them, read this article.  Before you call a professional, empower yourself with information.

Every year, thousands of homeowners ask, “What’s wrong with my gas furnace?” If you’re in that situation, this article will arm you with information before you call a furnace company.  Knowledge is protection against being taken advantage of – though most repair professionals have sound ethics.  You will learn how to deal with some common furnace issues.

We are providing you with a furnace problems troubleshooting guide that you can use to understand what is wrong with your furnace.  It also will allow you to be proactive in ensuring that the furnace is repaired before it stops working.   Diagnose furnace problems on your own.

1. Furnace not working 

This is one of the most common furnace problems and is very frustrating.  If you attempt to set the temperature above what the temperature is currently set in the home and it doesn’t work, make sure the switch is turned on.  If it doesn’t work, the following may be why:  

• The circuit breaker is turned off; if the circuit continues to trip when it is put back on, the furnace most likely has a mechanical short.  The circuit breaker is off, and if the circuit continues to trip after it is turned back on, there is likely a wiring short in the furnace
• It’s possible that the thermostat isn’t set on “heat,” which is simple to check and fix.  The thermostat isn’t set to “heat,” which is easy to check and remedy
• If nothing else works, the furnace’s main circuit board/control board is faulty, which may be evaluated by an HVAC specialist.  The furnace’s main circuit board/control board is bad, an issue that can be diagnosed by an HVAC technician if nothing else solves the issue.

2. Change the furnace filter

One of the first things you want to check is the air filter.  Over time, furnace filters get dirty.  Dirt and dust can quickly clog the filter, which impedes airflow, worsens indoor air quality, and can even prevent the furnace from turning on in some cases.  If the furnace is not working, this can be why.  It must be installed properly as well. 

3. Check the thermostat

To test the furnace, make sure the thermostat is set to “heat,” and attempt to set it higher than the current room temperature.  Make sure it is set to “heat,” and try setting the temperature at least 5 degrees higher than the current room temperature.  If it does not turn on, try replacing the batteries.  You may also need to give it a good dusting inside with a paintbrush.  This is part of the annual furnace problems troubleshooting.  

Make sure your thermostat isn’t getting any misleading readings from sunshine, lights, ovens, space heaters, or any other heat source.  This may cause it to think the room is warmer that it is and not turn on.  

Check the location of your thermostat and make sure it isn’t receiving any false readings from sunlight, lamps, ovens, space heaters, or any other heat source.  If the thermostat is receiving the wrong input, it will send out the wrong output. 

4. Furnace is blowing cold air

This is another common gas furnace problem.  One more thing to try if the furnace is not producing heat, is to verify that it is receiving electricity by switching the fan switch from the “Auto” to the “On” position.  If the fan begins to spin, the furnace is receiving electricity.  If the furnace won’t produce heat, you can check to see if it is getting power by moving the fan switch from the “Auto” position to the “On” position.  If the fan comes on, then the furnace is getting power. The likely issues then are:

• The gas is turned off, so check the gas cock near the furnace to make sure it is parallel to the gas line, set to the on position
• You need a new gas control because it not working 
• The gas control valve isn’t opening and must be replaced
• The ignitor is failing and must be replaced
• The draft motor isn’t functioning, or the fresh-air intake is blocked, perhaps by snow or debris, and needs to be cleared

You may need to hire a professional to replace any parts that aren’t working but you can do the diagnosing of furnace problems yourself first to see what you can repair on your own.

5. Draft motor running but furnace won’t start

This common furnace issue can be troubleshot as well with a few simple steps. Sometimes referred to as an inducer motor, the draft motor draws gas from the furnace and releases it out the exhaust stack. The draft motor is also called the inducer motor. It pulls hot combustion gases through the furnace and out the exhaust stack. If it starts and then the furnace shuts down, the following may be the problem:

• You may need to get a new circuit board if the furnace motor has failed The motor or the board that controls it has failed and must be replaced.
• Check for a blocked exhaust chimney and remove any debris A blocked air intake or blocked exhaust chimney (snow, debris and bird’s nests are common causes) must be cleared.
• One of the issues discussed above with gas, gas valve and ignitor must be addressed.

6. Draft motor won’t start

The next step in our home furnace troubleshooting is to address the draft motor not working.  If the draft motor does not start, then you probably either have a thermostat issue, thermostat wiring problem, electrical issue, control board problem or a bad draft motor.  You may need professional advice. 

7. The flame starts but the furnace shuts off

If the burner starts making heat but soon shuts off without warning, the flame sensor isn’t working.  The senser may simply need to be cleaned well.  Alternatively, you may need to purchase a new one.  If the sensor has corrosion on it, sanding it might work, though replacing it is a longer-lasting fix.  This common furnace issue requires a little troubleshooting.  If it just needs to be cleaned, the homeowner can do it.  Otherwise, a repairman will need to be hired. 

8. The furnace turns on but the house isn’t warm

Your home should be very warm if you have the right sized furnace.  Ensure that the issue is not just that the furnace is too small.  If your furnace is properly sized for your home, then it should keep your home warm even in extreme cold.  If it runs constantly but isn’t providing enough heat, this is another common furnace problem.  The likely cause is:

• That you need to make certain your air filter is installed properly.  You may need a new one  The filter is the wrong type for your furnace and restricts airflow, so should be replaced.
• The filter is installed backwards, an issue that can be checked by looking for the arrows on the filter frame that show proper installation direction with the flow of air.
• Your air ducts may be leaking if they are making a lot of noise.  Have them sealed as soon as possible Air ducts are leaking, sometimes producing telltale whistling noises, and it is time to have them sealed.

9. Check the furnace flame

Your furnace flame should be a healthy blue colour, with perhaps a small yellowish tip.  If you see a blue flame, you can be confident that your furnace is using gas properly. The blue flame indicates that your gas furnace is burning the fuel safely and efficiently.

If the flame is red, yellow, purple, green, or any other colour than blue, contact a professional right away.  Never attempt to fix your furnace flame colour on your own. This is a common gas furnace problem that a homeowner should not repair. 

10.  Pilot light and gas valve

If your furnace is not working, this may be why.  If you check the furnace flame and it is out, you will need to relight it.  While you may manually relight the pilot, use caution and check your owner’s handbook for correct procedures.  While you can relight the pilot on your own, be extra careful and consult your owner’s manual for proper instructions.

Never try to relight the pilot without first turning off the gas for about 10-15 minutes.  Don’t forget to turn off the gas for around 10-15 minutes before attempting to relight the pilot.  If you continue to smell any gas, do not continue.  You may have a leak.  In which case, you should evacuate the household immediately, then call your gas company and the fire department from a safe distance.  This is one time you should not be diagnosing furnace problems. 

Your furnace is one of the most important items in your home.  It keeps you and your family warm and safe if it is running properly.  Do some routine furnace problems troubleshooting, and you will save a lot of money.  You will also have peace of mind.  

Sources

• Common Furnace Problems 

• HVAC for Beginners

• Trouble Shooting with the Pros