Furnace Turns On Then Shuts Off in Greater Vancouver

When a furnace turns on, runs for only a minute or two, then shuts off — only to repeat the same cycle — this is called short cycling and it is a sign something is preventing the system from completing a normal heating run.

What This Symptom Means

Short cycling means the furnace is not completing a full heating cycle. This wastes energy, creates uneven temperatures, and puts extra wear on the heat exchanger, blower, and ignition components. It almost always means a safety component is tripping or a component is failing.

Common Causes

• Clogged air filter — restricts airflow and triggers high-limit switch shutdown
• Oversized furnace — heats the space too quickly and satisfies the thermostat before completing a cycle
• Faulty flame sensor — shuts off gas after brief ignition
• Thermostat placement near heat source causing premature shutoff
• Cracked heat exchanger — causes overheating and safety lockout
• Blocked or closed vents restricting return airflow
• Faulty high-limit switch tripping prematurely

What Homeowners Can Check Safely

• Replace air filter if it has been more than 3 months since last change
• Ensure all return air grilles and supply vents are open
• Move thermostat away from direct sunlight, drafts, or heat-producing appliances
• Check furnace error light for blink codes

When to Call a Licensed Technician

Some furnace issues require a licensed HVAC technician. Do not attempt to open gas lines, replace internal components, or reset persistent lockouts without professional diagnosis.

• Flame sensor cleaning or replacement
• High-limit switch testing
• Heat exchanger inspection
• Thermostat calibration and placement assessment
• Furnace sizing evaluation if oversizing is suspected

Frequently Asked Questions

Is short cycling damaging my furnace?

Yes. Each startup cycle puts stress on the igniter, flame sensor, heat exchanger, and blower motor. A furnace that short cycles regularly will fail faster than one running normal cycles. It also raises gas bills since startups consume more fuel than steady operation.

How do I know if my furnace is oversized?

An oversized furnace heats the home very quickly, then shuts off before the air has circulated evenly. The house may feel stuffy and have uneven temperatures room to room. A licensed technician can perform a heat load calculation to verify whether the furnace is correctly sized for your home.

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