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Winter mornings in the San Fernando Valley can be chilly, and the last thing you want is to wake up to a cold house because your furnace won't turn on. Before you worry about expensive repairs, there are several simple checks you can do yourself. Many furnace problems have straightforward solutions that don't require a service call. This guide walks you through the most common reasons your heater might not be starting and what you can do about each one.
Is your furnace refusing to start? Don't wait in the cold—call (818) 446-2099 or fill out our online contact form for fast help from Kilowatt Heating, Air Conditioning & Electric.
Check Your Thermostat First
Your thermostat controls when your furnace turns on, so it's the first place to look when your heater isn't working. Sometimes the issue is as simple as incorrect settings or dead batteries.
Start by making sure your thermostat is set to "heat" mode rather than "cool" or "off." Check that the temperature setting is at least five degrees higher than the current room temperature. If you have a programmable or smart thermostat, verify that the schedule hasn't changed unexpectedly. Many thermostats have battery compartments—try replacing the batteries if your display looks dim or blank. Finally, make sure no one accidentally bumped the thermostat or changed the settings.
Inspect Your Circuit Breaker and Power Switch
Furnaces need electricity to run, even if they use gas for heating. A tripped breaker or switched-off power can stop your furnace completely.
Head to your electrical panel and look for any breakers in the "off" position or sitting between on and off. If you find a tripped breaker, flip it all the way off, then back on. Most furnaces have a dedicated power switch nearby that looks like a regular light switch—check that it's in the "on" position. This switch is often located on or near the furnace cabinet and sometimes gets turned off accidentally during cleaning or storage activities.
Replace Your Air Filter
A clogged air filter is one of the most common causes of furnace problems. When the filter gets too dirty, it restricts airflow and can cause your system to overheat and shut down as a safety measure.
Locate your filter (usually near where the return air duct connects to the furnace) and remove it. Hold it up to a light—if you can't see through it, it needs replacing. Most homes should change filters every 1-3 months, depending on factors like pets, allergies, and how often the system runs. Installing a new filter is simple: slide out the old one, noting the arrow that shows airflow direction, and insert the new filter with the arrow pointing toward the furnace. This small maintenance task can prevent many heating issues before they start.
Look at Your Furnace's Reset Button
Many furnaces have a safety feature that shuts them down if something goes wrong. The reset button gives you a chance to restart the system after it's had time to cool.
Find the reset button on your furnace—it's typically red or yellow and located inside the blower compartment. Press it once and wait a few minutes to see if the furnace starts. If the button pops out again immediately or within a short time, this signals a more serious problem that needs professional attention. Never press the reset button more than twice, as repeatedly resetting can mask underlying issues or cause damage to your system.
Check for Closed or Blocked Vents
Your heating system needs proper airflow to work correctly. Blocked supply vents or return air grilles can cause your furnace to struggle or shut down.
Walk through your home and make sure:
- All heating vents are open and not blocked by furniture, curtains, or rugs
- Return air grilles have at least several inches of clearance on all sides
- No vents have been closed in rooms you're not using (closing too many vents creates pressure problems)
- Registers aren't clogged with dust, pet hair, or debris
After checking vents, give your system a few minutes to see if airflow improves and the furnace kicks on. Good airflow helps your furnace run efficiently and prevents unnecessary strain on the equipment.
Examine Your Gas Supply (For Gas Furnaces)
If you have a gas furnace, an interrupted gas supply will prevent it from producing heat. This is especially important to check if you've recently had work done on gas lines or if other gas appliances aren't working.
Look for the gas valve on the pipe leading to your furnace—the handle should be parallel to the pipe when the gas is on. If the handle is perpendicular (at a right angle to the pipe), the gas is shut off. You can turn it back on by rotating the handle to align with the pipe. If you smell gas (a rotten egg or sulfur odor), leave your home immediately and call your gas company from outside. Never attempt to fix gas leaks yourself or turn on anything that could create a spark.
Inspect the Flame Sensor (Advanced Check)
For those comfortable with basic maintenance, a dirty flame sensor can prevent a gas furnace from staying lit. The flame sensor is a safety device that confirms the burners are producing flame.
Turn off power to your furnace at the breaker before attempting this. Locate the flame sensor—it's a thin metallic rod positioned in the path of the burner flames. Gently remove it (usually held by one screw) and wipe it carefully with fine-grit sandpaper or steel wool to remove any buildup. Reattach the sensor, restore power, and try starting your furnace. If you're not comfortable with this task, skip it and call a professional instead.
When to Call a Professional
While many furnace issues have simple fixes, some problems require trained technicians with specialized tools and knowledge. Attempting complex repairs yourself can be dangerous and may void your warranty.
Contact a professional if you experience:
- Strange noises like banging, screeching, or grinding coming from your furnace
- The smell of gas or burning plastic anywhere near your heating system
- Your furnace repeatedly shuts off after starting (short cycling)
- Visible rust, corrosion, or cracks in the furnace cabinet or heat exchanger
- Your pilot light is out and won't stay lit after relighting
- You've tried all the basic troubleshooting steps and the furnace still won't run
These symptoms can indicate serious issues like cracked heat exchangers, faulty gas valves, or failing motors. Professional heater repair ensures your system is fixed safely and correctly.
Prevention Tips for Future Reliability
Once you get your furnace running again, take steps to prevent future problems. Schedule annual maintenance before the heating season begins—technicians can spot small issues before they become big problems. Keep the area around your furnace clear of storage items, cleaning supplies, and flammable materials.
Additionally, mark your calendar to change air filters regularly, and consider upgrading to a programmable thermostat if you don't already have one. Listen to your furnace when it runs—unusual sounds often provide early warning signs of developing problems.
Get Your Heat Back On Today
When basic troubleshooting doesn't solve your furnace problems, the team at Kilowatt Heating, Air Conditioning & Electric is ready to help homeowners throughout Van Nuys and the San Fernando Valley. Our experienced technicians can diagnose and fix furnace issues quickly, so you don't have to spend another cold night in your home.
Whether you need a simple repair or it's time to discuss replacement options, we'll give you honest recommendations based on your specific situation. Call (818) 446-2099 or use our online contact form to schedule service today.