How to Identify and Replace Your Bryant Furnace Ignition Sensor

When Your Bryant Furnace Won't Stay Lit, the Flame Sensor Is Usually to Blame

Bryant furnace flame sensor replacement is one of the most common furnace repairs homeowners face — and the good news is it's one of the most straightforward fixes you can do yourself.

Here's the quick answer:

Turn off power at the breaker and close the gas valve.
Remove the access panel to reach the burner assembly.
Locate the flame sensor — a small metal rod with a ceramic base, mounted near the burners.
Unscrew the sensor, disconnect the wire, and pull it out.
Clean with 400-grit emery cloth if the rod looks coated or dull. Replace it if the porcelain is cracked or cleaning doesn't fix the problem.
Reinstall, restore power and gas, and test the furnace.

The part costs under $20. A professional repair runs $75–$250.

When a furnace lights for a few seconds and then shuts off — over and over — it's almost always the flame sensor failing to detect the burner flame. The control board interprets this as a safety hazard and cuts the gas. It's a smart system, but a dirty or failing sensor can trigger it even when everything else is working perfectly.

I'm Adam Wettach, owner of Admiral Plumbing, Heating & Cooling, and over the years I've seen bryant furnace flame sensor replacement rank among the top service calls we handle every heating season across Utah County. This guide walks you through exactly what to check, how to fix it, and when to call a pro.

Understanding Your Bryant Furnace Flame Sensor (LH680534)

The flame sensor in your Bryant furnace is a vital safety component disguised as a simple piece of metal. Typically carrying the OEM part number LH680534, this device features a thin, bent metal rod attached to a white ceramic insulator base, which is secured by a small metal bracket.

Though it looks like a low-tech wire, it performs a highly sophisticated job using a process called flame rectification.

When the furnace's control board sends an electrical current to the flame sensor, the electricity cannot ground itself because the air surrounding the metal rod is non-conductive. However, when the burners ignite, the extreme heat of the flame ionizes the air. This ionized air becomes a pathway for electricity, allowing a tiny alternating current (AC) to flow through the flame and convert into a direct current (DC) that grounds out through the burner assembly.

This microamp signal (usually between 1.5 and 4.0 microamps) tells the control board that a safe, stable flame is present. If the sensor is dirty or broken, the current cannot flow. The control board assumes the gas is flowing but hasn't ignited, immediately shutting down the gas valve to prevent unburned gas from filling your home.

This safety function is critical. Uncontrolled gas accumulation is a severe fire hazard, and malfunctioning fuel-burning appliances are linked to carbon monoxide risks. In fact, more than 200 people in the United States die every year from carbon monoxide produced by malfunctioning fuel-burning appliances such as furnaces. Keeping this safety loop intact is paramount to protecting your family, which is why we emphasize checking this component during our Top 5 Common Furnace Problems and How to Fix Them evaluations. You can learn more about how this system operates in our Bryant Furnace Flame Sensor Location and Replacement Guide - Pick Comfort .

Locating the Sensor on Mid-Efficiency vs. High-Efficiency Models

Finding the flame sensor inside your Bryant cabinet depends entirely on the design of your heating system:

Mid-Efficiency (80% AFUE) Furnaces: These units feature a standard metal burner box that is open to the surrounding air. The flame sensor is incredibly easy to spot. It is mounted directly on the far-left or far-right burner panel (opposite the hot surface igniter) and protrudes directly into the path of the flame.
High-Efficiency (90%+ AFUE Condensing) Furnaces: High-efficiency models utilize a sealed burner box to maximize combustion efficiency. To find the sensor here, you must first unscrew the plastic or metal access cover of the sealed combustion chamber. Once inside, look near the burner assembly closest to the draft inducer motor. The sensor will be positioned in front of the final burner slot.

No matter the model, the sensor is always positioned so that the metal rod sits directly in the path of the fire when the burners are active.

OEM vs. Aftermarket Flame Sensors

When purchasing a replacement, you will face a choice between factory-authorized Original Equipment Manufacturer (OEM) parts and universal aftermarket sensors.

We strongly recommend opting for OEM Bryant/Carrier parts like the LH680534. OEM parts are manufactured to the exact dimensions, rod lengths, and bend angles required for your specific burner box. This ensures that the rod sits precisely in the hottest part of the flame, maintaining peak energy efficiency and preventing nuisance shutdowns.

Additionally, using factory-authorized parts preserves your system’s 10-year parts limited warranty. Universal aftermarket sensors are cheap and convenient, but if the rod length or mounting bracket is even slightly off, the sensor may fail to detect the flame reliably, leading to repeated system lockouts.

Bryant Furnace Flame Sensor Replacement: When to Clean vs. Replace

Before running out to buy a new part, it is helpful to know whether your sensor simply needs a quick cleaning or if it is time for a complete replacement.

Condition	Action Required	Explanation
Slight soot or white silica buildup	Clean	Normal oxidation from combustion; can be polished off easily.
Cracked ceramic/porcelain insulator	Replace	Electrical current will leak through the crack, causing false readings.
Bent, warped, or rusted metal rod	Replace	Structural damage prevents proper positioning in the flame.
Sensor is over 5 years old and failing	Replace	Sensors degrade over time and have a typical lifespan of 5 years.
Fails to work after two thorough cleanings	Replace	The internal connection or rod surface has degraded past repair.

As noted above, a typical furnace flame sensor has a lifespan of about five years. Given that a quality Bryant furnace can last between 15 and 30 years, you should expect to perform a bryant furnace flame sensor replacement once or twice over the lifetime of your heating system.

If you want to read more about diagnosing these specific issues, check out our guide on How to Tell If Flame Sensor is Bad - Furnace Repair and Troubleshooting Guide as well as our deep dive into Furnace Flame Sensor Problems and Fixes.

Signs You Need a Bryant Furnace Flame Sensor Replacement

How do you know when your flame sensor is crying out for attention? Watch for these common warning signs:

Short Cycling: The furnace turns on, the draft inducer runs, the igniter glows, and the burners light beautifully — only to extinguish exactly 4 to 7 seconds later. The system will try this three times before entering a hard lockout.
Bryant Error Code 31: Modern Bryant control boards feature a flashing LED light that communicates system diagnostics. A Code 31 (three short flashes, one long flash) indicates an ignition or flame sensing fault.
Yellow Burner Flames: Healthy burner flames should be a crisp, steady blue. If you see lazy yellow flames, your burners are dirty, producing soot that rapidly coats the flame sensor and prevents it from conducting electricity.
Rusted Flue Lines or Moisture: Poor combustion venting can cause moisture to back up into the burner cabinet, leading to accelerated rust on the burners and the flame sensor rod.
High Heating Bills and Cold Air: When a sensor is dirty, the system struggles to maintain a consistent heating cycle. This constant starting and stopping wastes fuel and reduces system efficiency by up to 15%.

For step-by-step instructions on diagnosing these exact symptoms, refer to How to Replace a Furnace Flame Sensor: A Step-by-Step Guide .

Step-by-Step Bryant Furnace Flame Sensor Replacement Guide

If you have diagnosed a bad sensor and purchased a matching OEM replacement, follow these steps to install it safely:

Step 1: Turn Off Power and Gas. Safety is non-negotiable. Switch off the electrical power to the furnace at the dedicated breaker panel or the service switch located on the side of the furnace cabinet. Then, turn the manual gas valve knob to the "OFF" position.
Step 2: Remove Access Panels. Take off the upper cabinet doors of your furnace to expose the burner compartment. If you have a high-efficiency model, unscrew the cover of the sealed burner box.
Step 3: Locate and Disconnect the Sensor. Find the flame sensor on the burner assembly. Gently pull the single wire connector off the spade terminal at the base of the sensor.
Step 4: Remove the Mounting Screw. Use a 1/4-inch nut driver or socket wrench to remove the single screw holding the mounting bracket to the burner wall. Keep this screw in a safe spot!
Step 5: Pull Out the Old Sensor. Gently slide the metal rod out of the burner box, taking care not to hit the surrounding metal or crack the ceramic base if you plan to keep it as a temporary backup.
Step 6: Install the New Sensor. Slide the new OEM Bryant sensor into the mounting hole, aligning the bracket with the screw hole. Tighten the 1/4-inch screw until snug (do not overtighten, as this can crack the ceramic base).
Step 7: Reconnect and Test. Reattach the electrical wire to the spade terminal. Replace the burner box cover and cabinet doors. Restore the gas supply and turn the electrical power back on. Set your thermostat to call for heat and verify that the burners ignite and stay lit through a complete heating cycle.

How to Test and Clean Your Flame Sensor Safely

If your sensor is structurally sound but coated in soot, a thorough cleaning can save you the cost of a replacement. However, you must handle this delicate part with care to avoid ruining it.

First, take proper safety precautions. Ensure the power is completely disconnected and the gas is off. Let the furnace sit for at least five minutes to allow any residual heat to dissipate from the burner box.

To clean the sensor, use a fine abrasive like 400-grit to 600-grit emery cloth or sandpaper. Gently rub the metal rod to polish away carbon deposits, soot, and white silica buildup until the metal looks bright and clean.

Warning: Never use coarse sandpaper or a heavy metal file. Coarse abrasives create deep scratches and grooves in the metal rod. These grooves act as magnets for carbon buildup, causing the sensor to fail again within a matter of weeks. Once polished, wipe the rod with a clean, dry microfiber cloth to remove any leftover dust or oil from your fingers.

If you want to verify whether the sensor is actually sending a signal, you can test it using a digital multimeter capable of measuring microamps ($\mu$A):

Set your multimeter to the $\mu$A DC setting.
Disconnect the wire from the flame sensor.
Connect one multimeter probe to the flame sensor's terminal and the other probe to the wire you just disconnected (this places the meter in series with the circuit).
Turn the furnace power on and call for heat.
As the burners ignite, watch the meter display. A healthy Bryant furnace flame sensor should read between 1.5 and 4.0 microamps (typically hovering around 3.5 $\mu$A). If the reading is below 1.0 $\mu$A or drops to zero, the sensor is dirty, misaligned, or completely dead.

For community discussions and troubleshooting logs from fellow homeowners who have tackled this exact diagnostic process, read through the Bryant Flame Sensor | DIY Home Improvement Forum . If you prefer to leave electrical testing to certified professionals, consider booking our Routine Furnace Maintenance Services to keep your system running safely.

Frequently Asked Questions About Bryant Flame Sensors

Can I clean a Bryant flame sensor with steel wool?

Yes, you can use fine steel wool to clean the sensor rod, but we generally advise using a fine-grit emery cloth or 400-grit sandpaper instead. Steel wool can break apart during cleaning, leaving microscopic metallic fibers on the ceramic insulator or the rod itself. When the furnace fires up, these metal fibers can cause an electrical short circuit, tricking the control board into thinking there is a flame present when there isn't, resulting in an immediate safety lockout.

What is the difference between a flame sensor and a thermocouple?

While both are safety devices designed to detect fire, they use completely different technologies:

Flame Sensors are used in modern furnaces with electronic ignition systems. They use electrical conductivity (flame rectification) to detect the presence of a burner flame.
Thermocouples are found in older furnaces with standing pilot lights. A thermocouple consists of two different metals joined at a junction that generates a small millivolt electrical current when heated physically by the pilot flame.

Why does my Bryant furnace shut off after 5 seconds?

If your furnace shuts off after exactly 5 seconds, it is experiencing a safety shutdown due to a lack of flame confirmation. The igniter lights the gas, but because the flame sensor is either dirty, broken, or disconnected, the control board never receives the microamp signal confirming the fire. To prevent unburned gas from building up inside your home, the board shuts down the gas valve and triggers a system lockout.

Conclusion

A malfunctioning flame sensor can quickly turn a cozy winter evening into an icy headache. Fortunately, with a little patience, some 400-grit emery cloth, or a replacement OEM Bryant sensor, you can easily restore warmth and safety to your home.

However, if you have cleaned or replaced the sensor and your furnace still refuses to stay lit, there may be deeper issues at play — such as a faulty control board, a failing gas valve, or a compromised heat exchanger.

When DIY troubleshooting reaches its limit, the team at Admiral Plumbing, Heating & Cooling is here to help. Serving Provo and the surrounding Northern Utah communities, we bring an A+ BBB rating and dependable 24/7 emergency service to every job. We will quickly diagnose your heating system, perform necessary safety checks, and get your home back to a comfortable temperature in no time.

Don't spend the night shivering! Reach out to us for Professional Furnace Repair Services or Schedule Professional Bryant Furnace Services today.

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