You turn up the thermostat and wait for the familiar sound of your furnace starting. A few minutes pass, but nothing happens. The temperature inside your home keeps dropping, and now you’re wondering whether you need furnace repair.
A furnace that won’t turn on doesn’t always mean there is a major problem. Sometimes the cause is something simple, such as an incorrect thermostat setting, a tripped circuit breaker, or a dirty air filter.
Before calling an HVAC technician, there are several things you can safely check yourself. If these basic troubleshooting steps don’t get your furnace running again, it’s time to have a professional diagnose the problem.
Start with the simplest possibilities before assuming there is a problem inside the furnace. These seven steps can help you rule out some common causes.
Start at your thermostat.
Make sure it is set to “Heat” and that the temperature is set higher than the current temperature inside your home. If the thermostat is set to 68 degrees and the room is already 69 degrees, for example, the furnace won’t have a reason to turn on.
If your thermostat uses batteries, check whether they need to be replaced. A blank or fading display can be a sign of weak batteries.
If you have a programmable or smart thermostat, check its schedule as well. A programmed temperature change could make it seem like the furnace isn’t working when the thermostat simply isn’t calling for heat.
After adjusting the thermostat, give the system a few minutes to respond. Some heating systems don’t start immediately after the thermostat calls for heat.
If the thermostat appears to be working normally but the furnace still doesn’t respond, move on to the next step.
Even if you have a gas furnace, it still needs electricity to operate.
Electricity powers components such as the blower, controls, and other parts that allow the heating system to function. If the furnace loses electrical power, it may appear completely dead.
Look for the furnace power switch. It is often located on or near the furnace and may look similar to an ordinary light switch.
Make sure the switch is in the “On” position.
Because these switches sometimes look like regular light switches, someone can accidentally turn one off without realizing that it controls the furnace.
If the switch is already on, check your electrical panel.
Find the breaker that controls your furnace or HVAC equipment and see whether it has tripped.
If you are comfortable doing so, you can reset a tripped breaker once.
If the furnace begins operating normally afterward, continue to pay attention to the system. If the breaker trips again, don’t keep resetting it.
A breaker that repeatedly trips can indicate an electrical problem that needs professional attention. Continuing to reset the breaker doesn’t solve the underlying issue and could create a safety concern.
Your furnace needs proper airflow to operate correctly.
A filter that becomes heavily clogged with dust, pet hair, and other debris can restrict airflow through the system. In some situations, restricted airflow can contribute to overheating and furnace shutdowns.
Remove the filter and inspect it. If it is obviously dirty, replace it with the correct type and size for your system.
Pay attention to the airflow arrow printed on the replacement filter so you install it in the correct direction.
Changing a dirty filter is good routine maintenance, but don’t assume the filter is responsible for every furnace problem. If you replace it and the furnace still won’t operate correctly, there may be another issue that needs diagnosis.
Take a quick walk through your home and check the supply and return vents.
Furniture, rugs, curtains, boxes, and other household items can sometimes block airflow without anyone noticing.
Make sure air has a clear path through the vents and returns.
Blocked vents may not explain a furnace that has completely lost power, but airflow problems can affect how the heating system operates. Keeping vents clear is also important for maintaining consistent comfort throughout your home.
If your furnace still isn’t working, listen carefully when the thermostat calls for heat.
What the furnace does next can provide useful information.
If absolutely nothing happens, the problem could involve the thermostat, electrical supply, controls, or another part of the system.
If you hear clicking but the furnace doesn’t start, the system may be attempting to begin its normal startup process but failing before it can produce heat.
If the furnace starts and then shuts off again after a short time, it may be short cycling or shutting down because a safety control has detected a problem.
You may also notice that the blower runs but the air coming from the vents isn’t warm.
You don’t need to diagnose these symptoms yourself. Simply paying attention to what the furnace does can give your HVAC technician useful information when you call for service.
Many modern furnaces have diagnostic features that can provide information when something goes wrong.
Depending on your equipment, you may see an error code on a display or a small indicator light that flashes in a particular pattern.
If the code or indicator is visible without removing furnace panels, write it down. Your owner’s manual may explain what the code means, or you can provide it to your HVAC technician when scheduling service.
Don’t remove panels or take apart the furnace just to find an error code. If the information isn’t easily visible, leave further diagnosis to a professional.
Sometimes the furnace isn’t completely dead. Instead, it starts normally, runs for a short period, and shuts off before your home reaches the temperature set on the thermostat.
It may then start again a few minutes later and repeat the process.
This is often referred to as short cycling.
Short cycling can have several possible causes, including airflow restrictions, overheating, thermostat or control problems, and issues with furnace components.
Repeated shutdowns may also indicate that a furnace safety control is doing its job.
If your furnace keeps shutting itself down, don’t repeatedly reset it or attempt to bypass a safety device to keep it running. Have an HVAC technician determine why the system isn’t completing a normal heating cycle.
The basic checks above can help you rule out simple problems, but there is a point when troubleshooting should stop.
It’s time to call an HVAC professional if:
At this point, the problem may involve components inside the furnace that require professional testing and diagnosis.
Checking a thermostat or replacing an air filter is very different from repairing a furnace.
Modern heating equipment includes electrical components, fuel-burning equipment, ignition systems, and safety controls. Attempting to repair these components without the proper training can be dangerous.
Homeowners should avoid trying to repair:
You should also never bypass a furnace safety control to force the system to operate.
Online videos can make furnace repairs look simple, but knowing how to replace a component isn’t the same as knowing why that component failed. Professional diagnosis helps identify the cause of the problem rather than simply addressing a symptom.
Stop troubleshooting immediately if you suspect a gas leak or your carbon monoxide alarm sounds.
If you smell natural gas, leave the home and move to a safe location. Avoid operating electrical switches or doing anything that could create a spark. Contact your gas utility or emergency services from outside and don’t return until authorities tell you it is safe.
Carbon monoxide is different because you can’t see or smell it.
If your carbon monoxide alarm sounds, get everyone outside into fresh air and contact emergency services. Don’t assume the alarm is malfunctioning.
A suspected gas leak or carbon monoxide problem is a safety emergency first, not a routine furnace repair.
A furnace that won’t turn on doesn’t always require emergency HVAC service.
The situation becomes more urgent when outdoor temperatures are freezing and the temperature inside your home is falling quickly. A prolonged loss of heat can also increase the risk of frozen pipes.
The people inside the home matter as well. Infants, older adults, and others who are especially vulnerable to cold may make a no-heat situation more urgent.
Gas odors, carbon monoxide alarms, smoke, burning smells, or signs of an electrical problem should always be treated seriously.
If there is no immediate safety concern and outdoor temperatures are mild, you may be able to schedule a regular furnace repair appointment. During freezing weather, however, a complete loss of heat may require emergency HVAC service.
If your furnace won’t turn on, start with the simple things.
Check your thermostat, furnace power switch, circuit breaker, air filter, and vents. Pay attention to what happens when the system tries to start and make note of any error codes you can see without opening the furnace.
If those steps don’t solve the problem, don’t keep resetting the system or start taking the furnace apart. It’s time to have the problem professionally diagnosed.
Air Systems Heating and Cooling provides furnace repair in New Brighton and surrounding western Pennsylvania communities. For urgent heating problems that can’t wait until regular business hours, 24-hour emergency HVAC service is also available.
If your furnace won’t turn on, contact Air Systems Heating and Cooling to have your heating system inspected and get your home comfortable again.
There are several possible reasons. The thermostat may not be calling for heat, the furnace may have lost power, a circuit breaker may have tripped, or there may be a problem with the furnace itself. Start with the thermostat and electrical supply before calling for professional diagnosis.
A severely clogged filter can restrict airflow through the heating system. In some furnaces, airflow restriction can contribute to overheating and cause the system to shut down. Replace a heavily dirty filter, but have the furnace professionally inspected if the problem continues.
Clicking can mean the furnace is attempting part of its normal startup process but isn’t successfully starting. Several different components can cause this behavior, so professional diagnosis may be necessary if the furnace continues clicking without producing heat.
A furnace that repeatedly starts and stops may be short cycling or shutting down because of an airflow, control, overheating, or other equipment problem. Don’t repeatedly reset the furnace or bypass safety controls. Have an HVAC technician identify why the system is shutting down.
Follow the reset instructions provided by your furnace manufacturer if a reset is appropriate for your equipment. However, don’t repeatedly reset a furnace that continues to shut down or fails to start. Repeated failure is a sign that the underlying problem needs to be diagnosed.
Carbon monoxide is a colorless, odorless gas that can cause serious illness or death. If you would like additional information about carbon monoxide symptoms, prevention, and safety, visit the CDC’s Carbon Monoxide Poisoning Basics.
