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?
Typically, a furnace won’t turn on because of one of these common issues:
Malfunctioning thermostat: This is the first thing to check. Ensure the thermostat is set to heating mode and at a temperature higher than that reflected on the thermostat. Digital thermostats can also lose programming (i.e., fail to retain temperature and time settings and reset) during power outages when backup batteries aren’t routinely changed.
Tripped circuit breaker or blown fuse: Gas and propane furnaces require electricity. If nothing’s happening when you’re expecting the whir of a blower, check the circuit breaker and fuse. At your electrical panel, make sure all switches related to the HVAC system are on. Reset any tripped breakers and replace all blown fuses, and your furnace should kick back on.
Dirty air filter: A clogged air filter can restrict airflow and cause your furnace to shut down or fail to start properly. Check your filter and replace it if it looks dirty, clogged, or hasn’t been changed in the last few months.
Full drain pan or clogged condensate line: High-efficiency furnaces produce condensation. If the drain pan is full or the condensate line is clogged, a safety switch may stop the furnace from turning on. Make sure the drain is clear, and the pump is working properly.
Gas supply leaks: If you smell gas, leave the area immediately and contact your gas company for emergency services. Gas leaks can lead to explosions. When your furnace won’t provide heat, ensure your gas supply valve is open and leaks (that rotten egg smell) are not present.
Pilot light problems: Older furnaces reliant on pilot lights often have issues with the ignition source. Re-lighting pilot lights can be simple, but if they frequently go out, a larger problem best addressed by an HVAC technician is likely. A professional furnace inspection should identify and correct pilot light issues.
Dirty burners: Clogged burners won’t light and will burn less effectively if they do. Accumulation of dirt and grime is inevitable where burners aren’t properly maintained. A technician can inspect and clean all parts of your furnace’s burners. If your burners are clean and the furnace fails to ignite, your issue lies elsewhere.
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 don’t smell gas in the home, try another gas appliance (e.g., your stove). If it doesn't ignite, chances are it’s a supply issue.
Check your air filter: Regularly change your air filter. Clogged filters deprive your system of the oxygen it needs to operate efficiently.
Check the pilot light: Most older furnaces include pilot lighting instructions on the service panel. Modern furnaces usually won’t start without a functioning pilot.
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
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.
