Furnace Won’t Turn On? 7 Common Causes and Troubleshooting Tips
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We don’t ask a lot from our furnaces. When it’s cold outside, keep us warm inside. Simple.
Fortunately, when your gas furnace won’t turn on, it might be simple to get the heat cranking again. There are some common reasons why your furnace won’t start. Below, we’ll walk through the most common reasons a gas furnace won’t start and what you can do to restore heat safely. If you need professional service for your gas furnace, remember that A.J. Perri has spent more than five decades servicing HVAC systems in the New Jersey area and is just a call away.
Why Won’t My Furnace Turn On?
When a furnace will not start, first check that the thermostat is set to Heat above the current room temperature, the furnace power switch and circuit breaker are on, and the air filter is not clogged. If these checks do not restore heat, the cause may be a condensate drainage problem, faulty ignition system, dirty flame sensor, gas supply issue, or furnace safety lockout.
Do not continue troubleshooting if you smell gas, hear gas escaping, or a carbon monoxide alarm sounds. Leave the home immediately and contact the gas utility or emergency services from outside.
Furnace Won’t Start Troubleshooting Guide
What you notice | Possible cause | Recommended next step |
|---|---|---|
The thermostat is blank or unresponsive | Dead batteries, incorrect settings, or loss of power | Replace the batteries if applicable. Set the thermostat to Heat and raise the setting above the current room temperature. |
Nothing happens when the heat is turned on | The furnace switch is off, or the circuit breaker has tripped | Confirm that the furnace power switch is on. Reset the breaker once. If it trips again, schedule professional service. |
The furnace starts and quickly shuts off | A clogged filter, restricted airflow, or furnace safety lockout | Replace a dirty filter and make sure the vents are open. Schedule an inspection if the problem continues. |
There is water near a high-efficiency furnace | A clogged condensate line, full drain pan, or failed condensate pump | Turn the system off and have the drainage system inspected. |
The furnace clicks but does not ignite | A faulty ignitor, dirty flame sensor, control problem, or interrupted gas supply | Schedule professional furnace service. |
The pilot light on an older furnace will not stay lit | A pilot assembly, thermocouple, or gas-supply problem | Follow the manufacturer’s instructions only if it is safe. Call a technician if the pilot repeatedly goes out. |
You smell or hear gas | A possible gas leak | Leave the home immediately. Do not operate switches or electronics. Contact the gas utility or emergency services from outside. |
How to Fix Your Furnace
There are several simple steps related to the issues above that can resolve your furnace troubles:
Check your thermostat: Make sure it’s set to heating; that the temperature setting is higher than the air temperature; and that the digital thermostat programming is intact.
Check your circuit breakers: Reset any tripped breakers.
Check your fuel supply: If you do not smell gas, you can check whether another gas appliance is operating to determine whether there may be a broader supply interruption. If you smell or hear gas, do not test appliances, operate switches, or attempt to restart the furnace. Leave the home immediately and contact the gas utility or emergency services from outside.
Check your air filter: A clogged air filter restricts airflow and may cause the furnace to overheat and shut down as a safety precaution.
Check the pilot light: Older furnaces may use a standing pilot light, while most modern gas furnaces use an electronic ignition system. If the furnace repeatedly fails to ignite, have an HVAC technician inspect it.
Check the drain pan: A full drain pan can trigger a float switch that prevents your furnace from starting. The drain should be clear, and the pump should be functioning correctly.
When to Call an HVAC Professional
Some furnace problems require professional repair. Call an HVAC technician if:
You smell gas in your home
Your furnace repeatedly trips the breaker
The system starts and shuts off quickly
The blower runs, but no heat comes out
Your furnace makes loud banging or clicking noises
Your furnace still won’t turn on after troubleshooting
A trained technician can safely diagnose the issue and prevent further damage to your heating system.
Need Help Getting Your Furnace Running Again?
We hope these simple gas furnace troubleshooting steps will warm up your home. However, if your furnace still won’t turn on, the team at A.J. Perri is here to help.
Our experienced technicians have provided trusted heating repair services throughout New Jersey for more than 50 years. Contact A.J. Perri today to schedule furnace repair service.
