Furnace Won't Turn On
Furnace won't start at all? Check these common causes before calling for service. From thermostat issues to safety switches.
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Safety Warning
If you smell gas at any point, leave your home and call your gas company emergency line.
Understanding the Problem
A furnace that won't turn on at all is a serious problem, especially during cold weather. Before calling for emergency service, there are several things you can check that might get your heat running again. The most common causes of a completely unresponsive furnace are electrical issues, thermostat problems, or tripped safety switches—many of which you can check yourself.
Common Symptoms
You might be experiencing this problem if you notice:
- No response when thermostat calls for heat
- Furnace is completely silent
- No blower, no ignition attempt
- Thermostat display is blank
- Furnace worked previously but now nothing
Possible Causes
This problem can be caused by several factors, listed from most to least likely:
Thermostat issues
Replace batteries, verify heat mode and temperature settings. If display is blank, check breaker to thermostat.
Tripped circuit breaker
Find the furnace breaker and reset if tripped. If it trips again immediately, don't reset—call a professional.
Furnace switch turned off
Locate the switch (usually on or near the furnace or at the top of basement stairs) and turn it on.
Safety switch tripped
Make sure all access panels are fully closed and latched.
Condensate drain clogged (high-efficiency furnaces)
Check for water in the drain pan. Clear the condensate drain line if clogged.
Control board failure
Professional diagnosis and replacement. Check for error codes if your furnace has a display.
Gas supply off
Verify the gas valve to the furnace is in the open position. Check other gas appliances to see if gas is flowing.
DIY Troubleshooting Steps
Before calling a professional, try these safe troubleshooting steps:
- 1
Replace thermostat batteries
- 2
Check thermostat settings (heat mode, temp above room temp)
- 3
Check and reset circuit breaker if tripped
- 4
Find and flip the furnace power switch
- 5
Make sure access panels are closed tight
- 6
Verify gas valve is open
- 7
Check for error codes on furnace display
When to Call a Professional
Contact a licensed HVAC technician if:
- Breaker trips repeatedly
- Error codes indicate specific failures
- You smell gas or burning
- All simple checks have been completed
- Furnace is in emergency/lockout mode
Prevention Tips
Help prevent this issue in the future with these maintenance tips:
- Know where your furnace switch and breakers are
- Keep condensate drains clear
- Schedule annual maintenance
- Replace thermostat batteries yearly
Estimated Repair Cost
* Actual costs may vary based on the specific cause, parts needed, and system type. We provide upfront pricing before any work begins.
Need Help With This Issue?
Our expert technicians can diagnose and fix this problem quickly.
Call (650) 540-7205Book Service OnlineQuick Facts
- Category:heating
- Urgency:Urgent
- DIY Fixes:6 of 7 causes
- Est. Cost:$0 (simple fixes) to $200-$600 (control board) to $500+ (other components)
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