Furnace Troubleshooting
Waking up to a cold home is frustrating but in many cases, your furnace might just need a quick check before you call a technician.
Here are the most common issues you can safely inspect on your own.
Important: If you smell gas, hear loud banging/whistling, or see flames behaving strangely, turn off the furnace and call a licensed HVAC technician immediately.
1. Check the Thermostat Settings
Many “furnace problems” start here.
Make sure:
It’s set to Heat
The temperature is higher than the current room temp
Batteries aren’t dead (for battery thermostats)
No schedules or “Eco” modes are overriding your settings
Try turning the thermostat off → wait 30 seconds → back to heat.
2. Make Sure All Vents Are Open
Closed or blocked vents restrict airflow and make the furnace shut down early.
Walk through your home and confirm:
Every vent is fully open
Furniture or rugs aren’t blocking them
Return grills are not clogged with dust
Good airflow = steady heat.
3. Inspect the Furnace Air Filter
A dirty filter can cause:
Weak heat
Furnace short cycling
Overheating
Safety limit switches shutting the system off
What to do:
Find the filter (usually near the blower compartment)
Replace if it’s dirty, clogged, or discolored
If you use a reusable filter, rinse with water and let it fully air-dry before reinstalling.
4. Check the Power Switch and Breaker
Your furnace needs electricity — even gas models.
Check:
The furnace power switch (looks like a light switch) is ON
The breaker for “Furnace” or “HVAC” hasn’t tripped
If the breaker trips again after resetting, stop and call a professional. This means there’s a real electrical issue.
5. Inspect the Furnace Flame (Older Models Only)
Gas burners should produce a steady blue flame.
If you see:
Yellow flames
Flickering flames
Irregular flame pattern
it may mean dirty burners or improper combustion.
Turn the furnace off and schedule a technician — this is not a DIY repair.
6. Pilot Light or Ignition Check
Depending on your furnace type:
Older Furnaces (Pilot Light)
If the pilot is out:
Turn the gas knob to OFF
Wait 1 minute
Turn to PILOT and relight according to the manufacturer instructions
If it keeps going out, you likely have a faulty thermocouple or gas issue → call a professional.
Modern Furnaces (Electronic Igniter)
Do not attempt to repair or clean the igniter yourself.
These are delicate and require an HVAC technician.
7. Verify the Gas Supply Valve
Locate the gas shutoff valve next to the furnace.
Make sure it’s parallel to the pipe (meaning ON).
If you recently had gas work done, a contractor may have turned it off.
When to Call a Professional Immediately
Stop troubleshooting and call an HVAC technician if:
You smell gas
The furnace makes loud banging, grinding, or whistling
Flame is yellow or irregular
The system keeps shutting off
Breakers keep tripping
The furnace won’t run even after basic checks
We can safely diagnose and repair the issue to get your home warm again.