10 Common Furnace Problems And How To Solve Them Easily

Sometimes, we just find ourselves, in a very random day, with a furnace problem without a single clue what really the issue is or how to fix it. You might be lucky to be caught up with this misfortune on a regular Summer day. But what if your furnace acts up in the middle of a freezing Winter?

In this blog, we listed the most common furnace problems homeowners face that we noticed over years of HVAC servicing. We added techniques on how you can check and troubleshoot it yourself with no tools or just your common house tools.

Clogged Filters

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Furnace filters MUST be regularly changed- at most every 3 months. But set a day every month to go and check it because in some cases, it might need changing sooner especially when the filter already turns grey.

A clogged filter can also manifest in a way in which your furnace is no longer heating your home sufficiently and HVAC repair services often get called for a furnace issue that is ca be fixed by a mere clogged filter change. Fortunately, you can easily change your furnace filters at home. This will save you time and money for unnecessary professional repairs.


Find your filter size. You can do this by sliding the old filter out of the filter cabinet located inside the furnace or the air return vent. Look for the filter dimension on the filter’s cardboard frame. If you can’t locate its dimension, note the model number and use it when purchasing new filters. Also, take note of the direction of the arrows in the filters, that indicates the furnace airflow and your new filters must be positioned in the same way like before.

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Install the new filter. Slide the new filter in the filter cabinet noting the printed arrows, it must point in the same direction as the old one and must be firmly placed in the compartment. And that’s that!

Furnace Operates in Short Cycles

If your furnace shuts off a few seconds after it is switched on, it usually indicates a problem with a faulty or dirty flame sensor. A dirty or damaged flame sensor won’t be able to sense the presence of heat and will command the furnace to shut down.


Check out this blog for a comprehensive article on flame sensor repair and replacement.

Faulty Thermostat

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If your furnace just shuts off then turns back at random times and intervals, then the fault may be traced back to a faulty thermostat. The thermostat works by dictating the furnace to turn on if the room temperature is below the desired temperature and it signals the furnace to shut off when the suitable temperature is achieved. So a broken thermostat may signal your furnace to switch on and off regardless of the indoor temperature.

Aside from that, a faulty thermostat can also cause the furnace to produce and maintain inaccurate temperature loads resulting in your home being too warm, too cold and just plain uncomfortable.


Look for the heat anticipator lever on your thermostat and set it one calibration mark closer to the “longer” setting. It may take some time before this takes effect, but if you noticed that your furnace still frequently turns on and off it is best to have your thermostat replaced.

Replacing the thermostat will usually solve the issue. Choose among our long list of high-quality thermostats for great comfort, ease and efficiency.

Furnace Blowing Not Enough Air

As mentioned above, when the furnace is not blowing off enough heat to keep your house warm, a clogged filter may be the cause but when you check and your filter is still in top shape then the problem may be a clogged blower wheel.


Clear the blower motor with any buildup that hampers its operation. We have a full blog on Furnace Blower Motor Troubleshooting and Replacement Guide to guide you on how to locate, open and take out the blower for you to clean it. It will also walk you through other possible issues your blower motor might be encountering and how to solve it.

Furnace Not Blowing Any Air At All

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If your furnace is running but it’s not blowing air, it might be a fan belt drive problem.


You should first check if there’s belt tensioning by pushing the fan belt down. There should be at least half an inch of room for extra movement. If the belt feels too tight or loose than normal, loosen the electric motor mounts and move the motor to create proper tension. Look for cracks in the belt as well. Constant heat exposure can cause the belt to crack. Cracked fan belts need to be replaced.

Normal Wear and Tear

Over time, it just normal when certain parts or components of your furnace wear down- it is inevitable and perfectly normal. That is why preventive maintenance is very important to properly support your furnace so it can live up to its expected lifespan that’s more than 15 years. Maintenance will also decrease the number of normal repair and replacement caused by wear and tear.


A yearly furnace tune-up can help your furnace solve existing issues it faces, and also aids identify, fix and prevent foreseeable problems and breakdowns that may arise in the future. In a separate blog, we discussed in detail why you need an annual furnace tune-up and how you can do it yourself.

Furnace Blows Cold Air

When a furnace blows cold air, it is most likely an ignition problem. With it failing, the furnace does not have any source of heating energy and thus unable to produce warm air for your home. In some cases, the presence of air bubbles in the gas line may cause certain delays on proper ignition.


Normally, to fix this problem, you only have to reset your furnace ignition by turning the central air system off through your thermostat then turning it back on after a few minutes. This will restart the whole operation and usually fix the problem.

In cases where air bubbles are present in the gas line, a professional HVAC contractor must be called for to do the job to ensure safety and efficiency.

Furnace Keeps Running

When the furnace blower motor or the furnace burners cease to stop, the furnace will also keep on running even though it already reaches the desired temperature set by the thermostat.


If the furnace blower motor won’t turn off, make sure the thermostat is switched to AUTO or OFF (not ON). If you try to turn the thermostat off, the blower must also turn off, otherwise, the problem is on the thermostat. Choose among our long list of high-quality thermostats to have your furnace run in normal operation again.

Check the thermostat to see if the Fan switch has been turned on. If it has, turn it to Off or to Auto. If it is set to Off or Auto, the furnace’s limit switch must be adjusted.

If the furnace burners won’t shut off, set the thermostat in a slightly lower temperature as setting it too high may cause the furnace burners to constantly run.

Furnace Leaks Water

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Newer high-efficiency furnaces as part of a central air system tend to produce water while heating thus drain pipes attached to the home’s drain system are installed for proper water drainage. When these drain pipes are clogged, water may leak. Another reason for a water leak may be a cracked collector box or heat exchanger.


This requires immediate attention from a professional HVAC contractor since it can compromise your furnace’s operations and can damage your home woodwork, ceilings and floors.

A quick fix you can do while waiting for the technician is to locate the drainpipe’s exit location and clear it of clogs.

Gas Leak!

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If you smell gas leaking from your furnace, do not light any fire, turn any switches and do not use you phone to call someone while inside the house. Evacuate immediately while leaving the door open if the smell is strong. Do not return to your home until you know it is safe and you have already called your gas utility or the fire department.


While waiting for the professionals, turn off the gas supply valve located by your gas meter on the gas inlet pipe by rotating the valve one-quarter turn with an adjustable wrench until valve’s oblong stem rests perpendicular to the supply inlet pipe.

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