If your gas furnace refuses to start up and you can't make it work no matter what you do, the appliance could be in lockout mode. When a component in your furnace fails, your furnace will automatically switch into lockout mode. Until you locate and repair the components in your furnace, it'll remain in lockout mode. Learn why your furnace may be in lockout mode and how you can unlock it below.

What's Lockout Mode?

Lockout mode is a safety mechanism or stage your furnace switches to when something goes wrong with its flame sensor, ignition system, or switches. Thermostat problems can also cause furnaces to lock. Once a furnace enters lockout mode, the appliance won't start up or restart until you repair the thing that caused it to shut off in the first place. 

Your furnace won't start or begin the process of heating your home until the thermostat tells it to do so. After the control board receives a signal from the thermostat to activate your furnace, it relays a short message to the ignitor, or ignition system, to create a small flame. The flame sensor checks the ignitor to see if it created a flame to light the burners or if it remained off.

A miscommunication between any of the components above can cause a lockout to occur. For example, a lockdown will occur if the:

• control board doesn't receive a timely signal from the thermostat
• ignitor fails to receive a message to light the flame sensor
• flame sensor fails to detect a flame in the ignitor

A lockout isn't something you want to address alone. A lockout can lead to fuel leaks in the system, or it can lead to complete furnace failure. An HVAC contractor can diagnose and repair the cause of your furnace's lockout for you. 

What Can You Unlock Your Furnace?

A contractor will take steps to isolate the cause of your furnace's lockout. The first step may include checking your home's thermostat to see if it lacks good batteries. A thermostat won't operate properly without fully powered batteries.

A contractor will also check the control board in the furnace during the visit. The control board contains electronic pieces that could melt or warp over time. If the control board is behind the lockout, a contractor will replace it.

If an HVAC contractor diagnoses your furnace with ignitor or flame sensor problems, they'll clean the components for you. The parts can quit if they become clogged with dust and other debris. The furnace should move out of lockout mode after the repairs. 

Learn more about furnace lockout mode by consulting a local ocmpany, like Myers Heating & Cooling.