Furnace Troubleshooting: 7 Common Problems & Fixes
When winter hits, the last thing you want is a broken furnace. But before you panic and call for emergency service, there are a few things you can try yourself. Many common furnace problems have simple fixes—especially if you're familiar with basic gas furnace troubleshooting.
At Miller’s Heating & Air, we’ve seen it all when it comes to troubleshooting furnace issues. Let’s explore the most common problems, what causes them, and how to fix them—or when to call in a pro.
1. Thermostat Troubles
Problem: Furnace not turning on or heating inconsistently.
Fixes:
Check thermostat batteries and replace if needed.
Make sure the thermostat is set to “heat” mode.
Set the temperature at least 5 degrees above the current room temperature.
Confirm date and time settings—some models operate on programmed schedules.
Sometimes your furnace isn’t the problem—it’s the thermostat.
2. Furnace Won’t Turn On
If your furnace isn’t powering on, here are a few steps to try before calling for HVAC service:
Circuit breaker: Look for a tripped breaker labeled HVAC or Furnace. Flip it off and back on.
Furnace switch: This wall switch looks like a light switch. Make sure it’s flipped on.
Furnace door: If the access panel isn’t shut properly, the door safety switch may prevent operation.
Gas furnace troubleshooting also includes checking:
Pressure switch: If this fails, your furnace may not ignite.
Blower motor: Burned-out capacitors or worn bearings can cause failure.
Gas line & valve: If gas isn’t reaching the system or the valve is stuck, the furnace can’t fire up.
3. Strange Furnace Noises
Banging, rattling, squealing, or humming could mean:
Loose or broken components
Motor or belt issues
Dirty burners or airflow blockages
Don’t ignore these sounds! While it’s okay to describe the noise and location, let a professional handle the fix.
4. Furnace Short Cycling
Short cycling is when your furnace repeatedly turns on and off without fully heating your home.
Common Cause: A clogged air filter is usually to blame. This restricts airflow, causing the furnace to overheat and shut off prematurely.
How to fix a furnace that’s short cycling:
Replace the furnace filter (ideally every 1–3 months)
Make sure vents are open and unblocked
Schedule a professional furnace maintenance tune-up if the issue persists
5. Dirty or Clogged Air Filter
This is one of the most overlooked furnace problems—and one of the easiest to fix.
Signs of a dirty filter:
Reduced airflow
Dusty indoor air
Furnace working harder and longer
A clean-looking filter may still be clogged with microscopic debris, so stick to a regular replacement schedule. Replace more frequently if you have pets or allergy sufferers in the home.
6. When to Call a Professional
While some gas furnace troubleshooting can be done DIY, other problems with your HVAC system need a trained technician:
Repeated breaker trips
Strange odors or gas smell
Ignitor failure
Pilot light won’t stay lit
Call Miller’s Heating & Air for fast, reliable furnace repair in Vancouver and Portland.
7. Prevent Furnace Problems with Maintenance
Annual preventative maintenance is your best defense against unexpected furnace failures. Benefits include:
Improved energy efficiency
Lower utility bills
Safer operation
Extended equipment life
Join our World Class Maintenance Plan to receive:
Annual furnace tune-ups
Priority service
Discounted repairs
Better indoor air quality
At Miller's, we offer our World Class Maintenance Plan, which includes an annual maintenance and safety check. Other benefits include priority service and discounts on services.
Best Furnace Repair in Vancouver,
Portland and Surrounding Areas
Heating equipment is complex. You should hire a licensed HVAC company to work on your HVAC system.
For the best furnace repair in Vancouver and Portland, reach out to MIller’s Heating & Air today!
