Furnace Lockout Mode Reset Help

The last thing anyone wants to deal with, when it is bitterly cold outside, is a furnace that stops working. Modern day high efficiency furnaces monitor a variety of conditions before, during and after the combustion process. If the furnace is unable to achieve ignition for a call for heat, or if an unsafe condition is detected, the furnace will enter what is called “lockout mode.” In many cases, an inoperable furnace that is locked out is the first sign unprotected or improperly guarded vents have allowed animals, debris or insects to enter the ventilation system and create a restriction. For this reason, we sell professional grade vent screens in our store to prevent costly and inconvenient furnace lockouts from easily avoided infiltration events.

What Does It Mean When the Furnace is in Lockout Mode?

Inside of Furnace Blower Compartment

As noted previously, furnaces monitor the entire heating cycle to ensure safe operating conditions exist. By utilizing sophisticated sensors, the controller will monitor the natural gas pressure, igniter and flame. However, most high efficiency furnaces will monitor the ventilation system, blower door state and many other important areas that all must be functioning properly to ensure that the furnace operates safely. When an unsafe condition is detected, the furnace’s controller issues a command to discontinue further attempted ignition cycles and ceases operation or just leaves the circulating blower running continuously. When this occurs, often after two or three failed restart attempts, the furnace is known to be in lockout mode and will not attempt to run again until the furnace is manually reset. It is important to note that there are soft and hard lockouts, which does vary by manufacturer.

Before jumping to the section on this page that details furnace lockout reset procedures, please view the important safety information and tips that follow underneath this paragraph. Not only do we want you to be safe, but we also want to help you identify what is causing the furnace to enter lockout mode so that it does not happen again.

Preventing Furnace Lockouts

Conditions to Consider Before Performing a Lockout Reset

If the controller on your furnace has detected an unsafe operating condition, or failure, you should first remedy the problem before performing a lockout reset. The reason for this is simple – your safety. Though everything may look alright with your furnace, only a professionally trained HVAC specialist can perform thorough sensor and control board testing, while of course ensuring adequate gas pressure and ventilation system functionality exists. Though certain conditions may exist that you can correct to get your furnace running safely again, as discussed below, a HVAC technician has the tooling and diagnostic equipment readily available to identify many electronic problems.

Identifying the Furnace Lockout Problem

Many furnace models have a visual display that will generate a visible status/error code. For example, some models will use a blinking L.E.D. to display a sequence of flashes that correspond with a specific fault code within the system. Some of these units will use a series of fast and slow blinks to display the code while more sophisticated units may display an easily read alphanumeric code. To determine what this status code means, please write down the code consult your owner’s manual or call the manufacturer directly. In most cases system lockouts occur because of a defective igniter, flame sensor, faulty pressure switch or limit switch. Though these conditions often require a technician to diagnose and service the furnace, there are other simple problems that you may be able to correct in an effort to get your furnace up and running without the need for assistance.

Correcting Conditions Causing Furnace Problems

Unobstructed Furnace Intake Vent

First, make sure your high efficiency furnace’s vents are not obstructed. Though people using the PVC vent screens sold in our store are less likely to encounter this problem, others with wide open vents are more likely to suffer from occasional blockages caused by leaves, animals and insects. Such blockages may also be accompanied by an odor (dead animal) or grinding sounds heard before the furnace stops functioning. Ice may also cause a blockage, which is normally an indication of improperly sloped PVC vent pipes. A visual inspection of the termination vents should reveal any sign of obstructions caused by leaves and traces of animal or insect activity. Clearing the leaves away from a vent is a simple process, unless they are lodged deep within the pipe. If you can see the leaves/debris, or suspect that the blockage is in close proximity to the termination vents, a shop vacuum may be used to collect the debris and clear the blockage. However, in many cases it is best to call a HVAC company to replace the clogged section of pipe. The presence of animal feces, food and/or dead insects is not a good sign and should be evaluated by a trained HVAC technician. In some cases a pest control specialist may need to be called in to deal with live animals or insects within the PVC pipe or furnace itself.

While you are checking the ventilation system for obstructions, don’t overlook the condensate drain line. If the condensate drain pipe becomes plugged, the furnace may detect a buildup of condensate in the secondary portion of the heat exchanger/drain box and actuate a pressure switch that disables the furnace for safety.

All furnaces need to have adequate ventilation and a dirty air filter can cause a system lockout to occur. For example, a clogged air filter may prevent an adequate supply of air from entering the system’s cold air return that causes the heat exchanger limit switch to trip. The remedy to this problem is simple – replace the air filter. It is always wise to replace your air filter annually or more often if occupants within your home have allergies or if environmental conditions cause more debris to get caught up in the filter.

Clean Flame Sensor

Another common problem that can cause a furnace lockout is a dirty flame sensor. The flame sensor comes into contact with the flame, and it is quite common for debris to buildup on it. In fact, most annual furnace inspections involve a technician cleaning the flame sensor as part of the preventative service visit. A furnace that cycles on and off quickly, especially after resetting a lockout, often has a dirty flame sensor. The flame sensor is located within the blower compartment (behind the upper compartment panel) and looks like a long metal rod. The flame sensor is usually held in place by a single sheet metal screw. With the power to the furnace off, the flame sensor can be unscrewed and removed/pulled outside of the blower compartment for cleaning. A mild abrasive can be used to clean the debris off of the rod. Under no circumstances should liquids be used to clean the sensor and care should be used to avoid touching the sensor with your hands. A suitable mild abrasive to clean the sensor would include a scour pad or steel wool. After the flame sensor is cleaned, it can be screwed back into its original position, the blower compartment door secured and power restored for testing.

Occasionally a defective blower door safety switch can cause the furnace to stop working. We’ve encountered a number of situations where manually pressing and releasing the safety switch was enough to get the furnace back up and running again. However, this fix is not common and often requires that the switch be replaced.

Though some problems with furnaces can be corrected by homeowners, more complex problems often require testing circuits for electrical power, testing capacitors and evaluating the circuit board. If you have gone through all the tips noted previously, and still can’t find the problem, chances are the problem is related to the electronics and should be corrected by a trained HVAC technician. If you did find a problem and corrected it, now it’s time to reset the furnace.

Furnace Lockout Reset Procedure

Though lockout mode errors and resets do vary from manufacturer to manufacturer, most use a simple reset procedure that involves turning power off to the furnace for thirty seconds or longer and turning it back. The interrupted power supply clears the lockout and will allow the unit to attempt normal operation again. However, some manufacturers have different or multiple lockout reset procedures. For example, some furnaces may be reset from lockout by reducing the call for heat setting on the thermostat for twenty-thirty seconds. Finally, some furnaces will reset themselves from lockout after a period of one or three hours has passed. Considering each manufacturer utilizes a specific lockout restoration process, it is wise to refer to your owner’s manual or contact the manufacturer directly.

Manufacturer Specific Lockout Reset Procedures and Contacts

When an unknown error code is displayed on the furnace, or for additional manufacturer and model related advice, it is a good idea to call the manufacturer. Most furnace manufacturers maintain support lines that are manned by trained support staff that can quickly provide assistance to customers. Because of this, along with manufacturer specific lockout resetting procedures, below we have provided additional helpful information so that you can view manufacturer specific information about your furnace. Please note that some manufacturers offer online symptom diagnosis and troubleshooting assistance, which you can locate by clicking on the company name (will open in new window) or by calling the listed manufacturer’s telephone number (where available). Most manufacturers also have installation instructions and owner’s manuals available for download, just in case you may have misplaced yours. Before visiting the manufacturer’s website or calling their technical support hotline for help, please have your furnace model and serial number readily available. In many cases the furnace model and serial number is printed on a sticker affixed to the side of the furnace cabinet.

Amana (https://www.amana-hac.com) Technical Support Number: 866-616-2664
American Standard (https://www.americanstandardair.com) Technical Support Number: 800-945-5884
Carrier (https://www.carrier.com/residential/en/us/) Technical Support Number: 800-227-7437
Coleman (https://www.colemanac.com) Technical Support Number: 877-874-7378
Ducane (https://www.ducanehvac.com) Technical Support Number: 800-448-5872
Goodman (https://www.goodmanmfg.com) Technical Support Number: 877-254-4729
Heil (https://www.heil-hvac.com) Technical Support Not Offered by Telephone
Lennox (https://www.lennox.com) Technical Support Number: 800-953-6669
Rheem (https://www.rheem.com) Technical Support Number: 800-432-8373
Ruud (https://www.ruud.com) Technical Support Number: 479-648-4900
Trane (https://www.trane.com/index.html) Technical Support Number: 800-945-5884
York (https://www.york.com) Technical Support Number: 877-874-7378

It is our hope that the information on this page will help you to resolve your furnace’s lockout problem. Should you have any questions regarding the information on this page, or if you would like to recommend additional information that will help others, please let us know by using our contact form.

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