Furnace Flame Sensor

Furnace Flame Sensor Replacement Guide 101: How To Replace Your Furnace Flame Sensor

As a homeowner, one of the most important things you need is to make sure your furnace and heating system are up-to-date. Everyone enjoys staying warm during the cold season with cozy home fires burning brightly inside. You may consider installing a flame sensor on your furnace in order not to miss any!

A furnace flame sensor is an essential safety device for residential homes. It senses if your furnace burner is on and provides feedback to the thermostat. This feedback tells the thermostat whether or not to turn on and off.

It is usually installed in furnaces to automatically shut off the fuel supply when the burner flame is extinguished. This ensures that you have enough oxygen flowing through your home to prevent the release of carbon monoxide into your house. Furnace flame sensors can also detect an issue with the gas flow or other problems with your heating system.

How Does a Furnace Flame Sensor Work?

Furnace Flame Sensor Work

The flame sensor detects the presence of burning gas or propane by measuring infrared light emitted from the combustion process.

It will trigger an electromagnetic switch that allows current to pass and power your furnace blower motor when enough heat comes through. If too much cooling occurs inside the chamber due to lack of fuel, this same device detects no flame and shuts off the blower motor to prevent overheating.

The optical interrupters used by furnace flame sensors are typically constructed from Pyrex glass (BK7) and aluminum. They’ve been designed to withstand high temperatures and will not rupture at any time, even after exposure to temperatures greater than 1150°C (2200°F) and at pressures above 1000 psi (68 bar).

The optical interrupters are powered by a direct connection to 12 V DC or 24 V DC sources through wires of different gauges. The power source is connected to the sensor through flexible cables or using a connector with a waterproof seal.

The connectors must be compatible with the type of cable used in the furnace, indicating it is consistent with the line used on the connector’s label.

The simplest form of a furnace flame sensor consists of two wires: one is attached to the burner, and the other is attached to the furnace’s metal housing or another ground point. When a flame is present, it causes a voltage difference between the wire attached to the burner and the wire attached to the housing, which generates power to flow through a relay, activating an alarm.

Furnace Flame Sensor Troubleshooting Tips

Troubleshooting furnace flame sensors involves checking everything from gas pressure to temperature and other related components of the appliance itself, such as an ignition system that is not working correctly.

Here are simple troubleshooting tips to help you out:

  • Please turn on the furnace, and there’s power entering through it. If you’re unsure, check with a multimeter for voltage at the wall outlet where your furnace is plugged in. Then test to see if voltage goes into your blower motor by removing the cover plate from one of its terminals – usually white or yellow. If the voltage reads around 115 volts and you still don’t have a flame, there may be a fault.
  • Check for continuity on your furnace’s thermostat wires to ensure they’re connected properly. You can do this by using a multimeter or simply checking that all wire leads are touching together when activated with the fan switch of your furnace.
  • Check for obstructions such as dirt buildup around your flame sensor. The central burner orifice can be clogged with slag, soot, dust, lint, or other debris, causing a delay between when you turn on your furnace and when it will ignite. It can also lead to a difference between the flame sensor reading and what is happening inside of your system.
  • Check the batteries on the thermostat if your home’s thermostat unit runs on batteries to see if they have gone flat. 

If the furnace flame sensor detects a flame, then there’s less chance of smoke filling the home if something goes wrong with your furnace system. 

How To Test Your Furnace Flame Sensor

Testing Furnace Flame Sensor

Test your furnace flame sensors annually, at least once per heating season, as part of your overall HVAC maintenance.

The pilot light is one of the easiest ways to test a furnace flame sensor. Find out what type of pilot light it has, then pull the pilot cord.

The pilot light should stay lit for 15 seconds or more (depending on your furnace) before turning off automatically or turning off manually. If the pilot stays on for less than 15 seconds, there may be a wiring problem on the furnace control board or an old pilot light that needs replacement.

If the pilot stays lit for 15 seconds but doesn’t turn off, check your thermostat settings first since many furnaces have thermostats that are too sensitive and may keep the pilot on long after the pilot light goes out. If it does turn off after 15 seconds, you probably have a faulty flame sensor. More likely, however, is that the sensor itself has broken down.

Check the temperatures at different levels ranging from 25 degrees F to 150 degrees F (in Fahrenheit degrees). A standard furnace should reach 450 degrees F at total capacity before venting outside air through an exhaust fan; if it’s below 250 degrees F at total capacity, this indicates either a problem with your firebox venting system or with your firebox itself.

Why You Should Replace Your Furnace Flame Sensor

When a furnace malfunctions, the cause is almost always traced to flame sensor malfunction. The flame sensor senses when the firebox ignites and can become faulty when it fails to operate, creating alarms in your heating system.

These alarms can result in frequent nuisance calls to your HVAC service provider.

Here are signs that you need to replace your furnace flame sensor.

  • When turned on, the furnace intermittently turns on and off or makes a continuous clicking sound. It’s an indication that the gas supply valve is faulty.
  • Despite the use of dehumidifiers, your home has excessive humidity in the winter. It can cause moisture buildup, which could lead to mold growth. High moisture levels in the air also significantly reduce the heating system, especially cold outside.
  • Your home feels stuffy despite the thermostat reading below normal temperature levels, even when set to a sleeping temperature. It can happen if there is moisture buildup inside your furnace, increasing your energy bills significantly.
  •  Your furnace’s air filter is dirty or clogged with dust particles, preventing airflow through the system despite its adequate size.
  • Your system is constantly cycling on and off to maintain a consistent temperature, even though your thermostat is set to one constant temperature for the entire day, resulting in unnecessary energy consumption due to short cycling.
  • Despite the presence of working flame sensors, your system is leaking gas into your home, causing a foul odor in the air. It can happen if faulty furnace flame sensors allow too much fuel to enter the venting system instead of just enough for combustion purposes only.
  • Your furnace’s pilot light requires frequent relighting, even though there are no problems with your gas supply or any other components in your system. It can indicate moisture buildup inside your venting system caused by faulty flame sensors. They do not detect when to shut off fuel, ultimately allowing excess amounts into the air.

How to Replace a Furnace Flame Sensor 

Replacing Furnace Flame Sensor

A faulty flame sensor can cause problems for your heating system and lead to higher energy bills.

These simple steps will take you 30 minutes to replace your furnace’s flame sensor.

  • Turn off the power and make sure that there isn’t any gas leaking, as this could be dangerous if it comes into contact with an open flame. 
  • With the mounting screwdriver and needle nose pliers, pull out your old sensor and detach its wire. 
  •  Place a new flame sensor into the opening using the mounting screwdriver, then attach the wire.

You can then switch the power back on by turning your furnace’s circuit breaker over from off to on again. 

Where to Buy Furnace Flame Sensors 

 Before purchasing one, consider your furnace model and the type of sensor you want to buy. Some flame sensors are more energy-efficient than others. Consider whether you want a wireless or wired sensor. Wireless sensors are easier to install. However, they may not provide optimal performance.

Here are some flame sensors from Amazon that you might consider for your furnace;

Goodman Replacement Flame Sensor Rod, part number SP208

Goodman Replacement Flame Sensor Rod

It could be that your furnace isn’t at its peak efficiency, depending on whether or not there is an accurate flame sensor inside. Goodman’s new line of flame sensors makes it easy for you to get up and running quickly by providing added safety and excellent performance every time.

The sensor is a direct replacement for part number 0130F00010—a replacement for the old-style number B11726-06. The rod measures 2 inches long, with a 1/4 inch Male Terminal for Wire Connection.

Pros of the Goodman Furnace Flame Sensor

  1. It can withstand extreme temperatures reliably.
  2. It’s accurate, easy to use, and guides you with factual time information.
  3. It can work on both AC and DC voltage.
  4. It is effortless to install.

Cons of the Goodman Furnace Flame Sensor

  1. It may not be compatible with all furnaces and require replacing the heating unit if it fails.
  2. It may not provide accurate information because they rely on radiation from the flame to sense its temperature. The problem is that radiation from other sources like red-hot burners can affect readings, and radiation from the flame reflects the sensor.

Goodman Furnace Flame Sensor B11726-06 | Amazon

This is a brand new Replacement that fits Goodman Furnace Flame Sensor B11726-06.

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03/10/2024 07:56 pm GMT

Lennox 52w2901



Lennox 52w2901

The upgraded replacement furnace flame sensor fits Lennox 52w2901. The device weighs ‎0.528 ounces, measures 6.61 x 3.39 x 2.13 inches, and no batteries are required. The sensor guarantees that your house will not get too cold in the winter and too hot in the summer.  No wiring modification is required. 

Pros of the Upgraded Replacement Lennox Furnace Flame Sensor

  1. It is easy to install using existing wiring; very little maintenance is required.
  2. It is reliable as it can detect combustion gas even if there is no blower or fan to help move air through the furnace.
  3. It provides instant feedback on the regular operation of the furnace.

Cons of the Upgraded Replacement Lennox Furnace Flame Sensor

  1. The sensor should be mounted at least 30 centimeters (12 inches) away from the flue side of the firebox and within 150mm (6 inches) of an air inlet for it to function correctly. It makes it unsuitable for use with large furnaces which require further installation, such as in industrial furnaces (up to 5 m³). 
  2. It is not suitable for forced draft furnaces or furnaces that are too close to each other because it cannot effectively detect combustion gases released from both furnaces simultaneously.

Furnace Flame Sensor | Amazon

Furnace Flame Sensor Replacement for Lennox 52W2901.

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We earn a commission if you make a purchase, at no additional cost to you.
03/11/2024 10:22 am GMT

Bryant Furnace Flame Sensor

Bryant Furnace Flame Sensor

The brand new, upgraded Bryant Furnace Flame Sensor allows you to connect it with any home heating system, including baseboard heaters, water heaters, boilers, furnaces, and gas stoves. 

When equipped with optional 1/8-inch mini-jacks, the sensor can also provide continuous monitoring for low voltage and power interruption, which can help you prevent unnecessary furnace failure and reduce energy waste.

Buy this product at $13.45 on Amazon.

Pros of the Bryant Furnace Flame Sensor

  1. This device prevents overheating and furnace damage, lowering maintenance costs.
  2. It’s also easy to use; hook it up to your existing thermostat, then mount it on top of your burner tube in front of your furnace.

Cons of the Bryant Furnace Flame Sensor

  1.  If you have limited space available in front of your furnace, you may need to purchase additional mounting brackets to install this correctly in front of your unit.
  2.  It needs calibration each time you replace one of your burners with a new one, forcing you to call an expert to come out and perform this task for you.

Bryant Furnace Flame Sensor | Amazon

This is a brand new replacement for Bryant Furnace Flame Sensor LH33WZ520.

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We earn a commission if you make a purchase, at no additional cost to you.
03/10/2024 05:42 pm GMT


Question: Should I Clean My Furnace Flame Sensor?

Answer: The combustion in the furnace causes a little bit of soot and other carbon deposits, which can stick to the rod. If there’s no flame or if they don’t get hot enough for your burner, then your control board will shut off gas valves. 
Follow the replacement instructions above to uninstall your flame sensor, clean using aluminum oxide, gently rub the metal rod with fine-grit sandpaper to prevent buildup. Use a clean cotton cloth to wipe it clean, then put it back.

Question: Where is My Furnace’s Flame Sensor Located?

Answer: The correct furnace flame sensor is installed in the vent opening between the unit blower and the burners. The furnace flame sensor activates an autogenic gas valve that shuts off the furnace’s fuel supply when it doesn’t need gas for heating.

Question: How Often Should a Furnace Flame Sensor be Replaced?

Answer: In a properly designed home heating system, you should replace your furnace flame every three years. In some scenarios, it can be more as long as the furnace is functioning.

Question: Which is the Best Type of Furnace Flame Sensor to Use in Residential Homes?

Answer: Most residential furnaces use photoelectric sensors to sense when gas flows through an open pilot light at low temperatures where other technologies may not work correctly. These sensors are very reliable and precise, but they don’t work well when the flame goes out due to wind conditions or draft issues.

Furnace Flame Sensor Replacement Guide: Conclusion

A flame sensor is essential for safety and ensures you don’t lose heat or air conditioning because of an improperly functioning heating system. If your furnace doesn’t have one, it’s time to replace it! Install this crucial part of any HVAC system and get you back on track.

You owe it to yourself—and your home–to ensure that everything runs smoothly all year round!

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