St. Louis winters often bring sudden temperature swings, which is when these issues are most common. Furnaces not serviced properly can struggle.
When the temperature drops suddenly, your furnace should respond by turning on and keeping your home comfortable. But if your furnace fails to start when it gets colder outside, it’s often a sign that something isn’t working properly.
This is a common issue for St. Louis homeowners—especially during cold snaps when furnaces are pushed harder than usual.
Why Temperature Drops Trigger Furnace Problems
A furnace that struggles or fails when temperatures drop usually isn’t reacting to the weather itself—it’s reacting to increased demand.
When it gets colder:
- Your furnace runs longer cycles
- Safety components are tested more frequently
- Airflow and exhaust systems are under higher stress
- Small issues that went unnoticed in mild weather become major problems
Common Reasons Your Furnace Won’t Turn On When It Gets Cold
1. Dirty or Clogged Furnace Filter
One of the most common—and most overlooked—causes.
When the filter is clogged:
- Airflow is restricted
- The furnace overheats
- Safety switches shut the system down to prevent damage
What to check: If your filter appears dirty or hasn’t been changed in 1–3 months, replace it and then restart the system.
2. Furnace Limit Switch Tripping
The limit switch protects your furnace from overheating. During extended run times in cold weather, it can trip if:
- Airflow is restricted
- Internal components overheat
- The furnace is aging or worn
Once tripped, the furnace may refuse to restart until it cools—or it may repeatedly shut down.
3. Thermostat Issues During Cold Weather
Cold snaps can expose thermostat problems, such as:
- Poor calibration
- Weak batteries
- Placement near drafts or exterior walls
- Faulty wiring
If the thermostat believes your home is warmer than it actually is, it may not send the signal to turn on the heat.
What to check:
- Replace thermostat batteries
- Make sure it’s set to “heat.”
- Increase the temperature setting by several degrees to test the response
4. Electrical or Control Board Issues
As furnaces age, electrical components become less reliable. Cold weather can expose:
- Weak connections
- Failing control boards
- Sensors operating out of tolerance
These problems often appear suddenly during a temperature drop.
5. Pressure Switch or Venting Problems
Your furnace must safely vent exhaust gases outside. Cold weather can cause:
- Ice buildup in the intake or exhaust pipes
- Snow blockage
- Condensation freezing inside vent lines
What You Can Safely Check Before Calling for Furnace Repair
Before calling an HVAC professional, homeowners can safely:
- Replace the furnace filter
- Check thermostat settings and batteries
- Make sure circuit breakers haven’t tripped
- Ensure intake and exhaust pipes are clear of snow or debris
When to Call a Professional Furnace Technician
You should schedule furnace repair if:
- The furnace won’t turn on at all
- The system shuts down repeatedly during cold weather
- You hear unusual noises or smell burning odors
- The thermostat calls for heat, but nothing happens
Furnace Problems During St. Louis Cold Snaps
St. Louis winters often bring sudden temperature swings, which is when these issues are most common. Furnaces that haven’t been serviced recently are especially vulnerable when overnight lows drop quickly. Regular maintenance helps catch airflow issues, failing parts, and drainage problems before cold weather exposes them.
Need Furnace Repair in St. Louis?
If your furnace isn’t turning on when temperatures drop, help is available. Thomas Hoffmann Air Conditioning & Heating LLC is a locally owned St. Louis HVAC company providing reliable furnace repair and maintenance. Contact us at (314) 471-7625 or via our online contact form.
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At Thomas Hoffmann Air Conditioning & Heating, we pride ourselves on being a locally owned and operated HVAC company. With more than 30 years of experience and a master technician and mechanical engineer as our owner, we can replace, repair, and maintain your business or home’s HVAC system.