How a Furnace Ignites Step-by-Step: From Start to Blower Running

When your thermostat calls for heat, your furnace doesn’t just magically turn on. It follows a precise, carefully orchestrated sequence designed to keep your home warm safely and efficiently. Knowing how your furnace starts can help you identify potential issues early, avoid costly repairs, and understand when it’s time to call a professional.

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🔧 Furnace Services: Tune-Up & Repair | Installation | Cleaning

Step 1: Inducer Fan Starts

The process begins with the inducer fan, also called the draft inducer. Its job is to:

• Clear exhaust gases from previous furnace cycles
• Create proper airflow through the vent system
• Ensure safe combustion conditions before ignition

Without the inducer fan, dangerous gases like carbon monoxide could linger, which is why furnaces never proceed until this step is verified.

Step 2: Pressure Switch Checks Airflow

Once the inducer fan is running, the pressure switch comes into play. This small, round device monitors airflow and confirms:

• The venting system is clear
• The inducer motor is operating properly

If the airflow isn’t correct — due to a clogged vent, dirty filter, or motor issue — the pressure switch prevents the furnace from igniting. Many furnaces will show a lockout error code on the control board to signal this problem.

Step 3: Igniter Activates

With airflow confirmed, the furnace moves on to ignition. There are two common types of igniters:

1. Hot surface igniter: Glows red-hot to ignite the burners
2. Spark igniter: Creates a spark to light the gas

This step ensures that the furnace is lighting safely and reliably.

Step 4: Burners Ignite & Flame Sensor Confirms Combustion

As the burners ignite, a flame sensor immediately checks for a stable flame. Its role is critical:

• Confirms gas is burning safely
• Prevents gas buildup if the flame isn’t detected
• Helps the furnace control board decide when to start the blower

If the flame sensor detects a problem, the furnace shuts down automatically, protecting your home from unsafe conditions.

Step 5: Blower Fan Starts

Once the flame is stable, the blower fan activates. It circulates warm air through your home’s ductwork, providing consistent comfort.

• Modern furnaces may have variable-speed blowers for energy efficiency
• Older units typically use a single-speed blower for simplicity

Proper blower function ensures your home warms evenly and your furnace runs efficiently.

Step 6: High-Limit Switch Ensures Safety

The high-limit switch is the furnace’s last line of defense. It monitors the internal furnace temperature and will shut the burners off if:

• The blower fails
• Airflow is restricted by a dirty filter or blocked vent
• The system overheats for any reason

This safety feature prevents damage to your furnace and avoids potential fire hazards.

Why Understanding This Sequence Matters

Knowing the step-by-step ignition process can help you:

• Identify furnace issues before they become serious
• Understand error codes and symptoms
• Decide when a professional service is needed

Regular furnace maintenance keeps all these systems functioning properly, including the inducer fan, pressure switch, igniter, flame sensor, blower, and high-limit switch.

Professional Furnace Services in Winnipeg

For homeowners in Winnipeg, staying ahead of furnace problems is crucial — especially during our long, cold winters. LIDOMA Home Services provides comprehensive solutions:

• ✅ Furnace Tune-Up & Repair
• ✅ Furnace Installation
• ✅ Furnace Cleaning

📞 Call today: +1 204 297 4420

Our licensed HVAC technicians inspect every step of your furnace’s ignition sequence, clean critical components, and make sure your system runs safely, efficiently, and reliably all winter long.

Conclusion

Understanding how your furnace starts — from the inducer fan to the high-limit switch — empowers you to recognize early warning signs and keep your home safe. Don’t wait for a breakdown. Schedule regular maintenance, cleaning, or professional repair with LIDOMA Home Services, and enjoy warmth and peace of mind this winter.