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Furnace Lockout: Causes and Solutions

Is your furnace leaving you out in the cold more often than not? Is it refusing to restart after several attempts to reset it? You may be experiencing a furnace ignition lock out.

What Is Furnace Lockout?

Today’s modern furnaces come equipped with various safety sensors that ensure its proper function. If these sensors detect a condition that is determined to be unsafe, the furnace will be forced to shut down to prevent any safety hazards or damage to your unit. While these safety measures are effective, your furnace is likely to remain in lock out until you or a professional technician reset it.

Many homeowners send a furnace into lockout mode after attempting to get it going several times without success. Furnace lockouts most commonly occur due to:

• Issues with a flame sensor
• Issues with the ignition mechanism
• Issues with a limit switch
• Issues with gas supply

Faulty Flame Sensors

A faulty flame sensor is one of the more common causes of a furnace lockout. As a furnace starts a cycle, a safety sensor checks for the presence of fire. If the safety sensor is defective, it will not detect a flame, and a control switch will halt the furnace ignition sequence. Most modern furnaces have a limit of four tries before it is triggered to go into lock out mode.

Faulty Ignition

If the furnace ignition switch does not activate within seconds, the controller switch will prevent the furnace from starting up. Gas furnaces go into lock out mode after a failure to light the main burners.

Limit Switch Issues

Furnaces contain limit switches that monitor heat temperatures and fuel pressure. Temperatures that are determined to be “out of safe range” trigger the shutdown, a lock out response to keep the furnace from reaching unsafe operating temperature and pressure levels.

Preventing a Furnace Lockout

Take these steps to prevent an untimely and inconvenient furnace lockout.

• Clean or replace flame sensors
• Clean and replace air filter
• Inspect and clean vent pipes

Performing a reset procedure is necessary when your furnace fails to restart, even after repeated attempts. Turning off power, waiting a few minutes, and turning the unit back on will cause it to recycle. Modern furnaces have an automatic renew period of 1-2 hours; you may be able to turn it on again after this period has passed. If these methods of resetting are not working for you, the best choice is to call a qualified HVAC technician to determine the cause of the lockout and make recommendations for repair and resetting.

We’ll Get You Running Again!

McFarland Indoor Comfort Services has the tools, knowledge, and service integrity to attend to all of your heating and cooling needs. Serving valued clients in Madison and St. Clair counties, we provide repair, replacement, maintenance plans, heat pump service, sheet metal fabrication, and commercial repair for all types of HVAC units. Contact us today, and we’ll get you up and running again!