How to Tell If Flame Sensor is Bad

Do you have a furnace at home that keeps shutting down and cannot give the heat to the entire house? one of the reasons that could happen is because the furnace flame is gone bad. There are three signs of a bad flame sensor. First, the furnace starts working but then quickly shuts down or also known as short cycles. Second, there are cracks in the porcelain of the flame sensor and third, you find the flame sensor is corroded.

It is recommended you contact an HVAC technician to fix the problem, however, you can do DIY diagnosis and clean the furnace flame sensor which could be the reason why your furnace stop working.

The Flame Sensor Purpose

First of all, we will need to understand first what the purpose of a flame sensor is. A flame sensor is used to know if there is a flame has produced in the furnace. If the furnace hasn’t fired and the gas valve is open, it will release the propane or natural gas. Worst scenario, the propane or gas can leak out and transfer into your house.

Gas leaking is very dangerous since it can cause an explosion. An explosion of gas leaking could happen when a water heater or gas stove is turned on. Always be cautious if you smell gas in your house, open all ventilation and do not turn on a gas stove and water heater until you are sure that there is no gas leaking.

To know if a flame sensor is still in good condition, it will shut down the gas valve when the furnace is not firing and there is no flame. To know if the flame sensor is in a bad condition, it will not sense the flame even the furnace is running properly, and a flame sensor will automatically shut down a furnace unit. This will cause the furnace will shut down quickly when it’s being turned on and will fail to give the heat to the entire house.

Flame Sensor Location – How to Find a Flame Sensor

If you want to find a flame sensor, first you will need to open the cover of furnace access. Please note that it could be protected in slots, and you may need to open a few screws. Check the manual book of your furnace because you may be able to identify the location easier.

Usually, the flame sensor is a rod made from metal and it has either white, yellow or brown porcelain which surrounds the rod in the end. The purpose of the porcelain is to protect the sensor from laying on the furnace frame made from metal. Depends on the brand and type of your furnace, some sensors are bending for 45 degrees, 90degree or straight close to the end.

The flame sensor usually located on the outside of the burner, usually it has a single wire that is attached to it. In most of the furnaces, the flame sensor overhangs into an open flame chamber or through the cover where the burning flame is located.

Please note that if you are not experienced in opening the furnace, it is strongly recommended that you contact an HVAC technician to diagnose and solve the issue.

DIY Flame Sensor Diagnosis

After you found the location of a flame sensor, you could do a DIY diagnosis of the flame sensor. First, you will need to make sure that you have already turned off the electrical power to your furnace. Turn off not only the switch on the furnace but also at the electrical box. Second, you will need to close the furnace gas valve and remove the mounting screw from the flame sensor.

Third, pull out the flame sensor and do it gently. Fourth, inspect it visually and see if you found any burnt or corrodes on the flame sensor. If this happens, the reason could be because the flame sensor is dirty and you can clean it.

If after cleaning, the furnace still stops working, you need to replace the flame sensor. If you find there is a crack or missing piece from the porcelain insulation, you will also need to replace the flame sensor with the new one.

After you finish replacing or cleaning the flame sensor, make sure that the flame sensor is remounted. You can turn on the power, have the gas valve opened and try to light the furnace. By knowing how to diagnose and clean the flame sensor, you will no need to wait for an HVAC technician to come and solve the issue. Not only saving your time, but you will also save the cost.

How to Clean a Flame Sensor

If you find that a flame sensor is dirty and you need to clean it, you can follow these following instructions. First, don’t forget to shut off the power as well as gas to the furnace unit. Second, after you locate the sensor, remove it so you can clean it.

Clean corrosion and soot from a flame sensor using an emery cloth with fine grit. Try to have the finest grit since it will give a better result. A fine grit from the emery cloth can avoid any indentation happened to the sensor flame since it is made from a soft metal

If you use a medium or coarse emery clothes and it causes grooves to the soft metal, it could accumulate carbon which comes from the burner flames. It will make the sensor will fail in a short time and you will need to clean it again. Therefore, using the finest grit will save you from cleaning the flame sensor in a short period.

Once you have finished cleaning the sensor flame, put it back in the original place and try to restart the furnace. If the furnace is still not working or stop in a short cycle, then you may need to replace the sensor flame.

How to Replace a Flame Sensor

To know if the sensor needs to be replaced, you can check if it’s damaged and if by cleaning it still doesn’t fix the problem. You can find the new flame sensor in the furnace parts store nearby. Take the broken sensor flame when you purchase the new one and don’t forget to check the information of the furnace such as brand, model and serial number.

If you live in an area in which it is difficult for you to find the furnace parts stores or suppliers, you also can buy the flame sensor online. There are many online HVAC parts shops or online repair clinic available, make sure you choose the reliable one. Call the customer service of the online shop will be the quickest way to purchase the right parts.

If the brand of your furnace is using universal parts, you don’t need to buy the exact parts from the brand. you can purchase the universal sensor flame which usually available in building suppliers, home depot and HVAC parts shop.

When you have the new flame sensor, you can replace it by yourself. First, you need to have the mounting screw to be removed and you can take out the sensor. Second, detach the single wire that is attached on the sensor then you can push the new sensor inside and secure it. Finally, make sure to attach the single wire to your new flame sensor.

What if Your Furnace Still Doesn’t Work?

The most problem of a furnace is it shuts down just a few seconds after it’s turned on. If you have already cleaned or replaced the flame sensor and it still doesn’t work, there could be other problems happen with your furnace. Some cases also happen that once you installed the new sensor flame, it will work for two weeks and the furnace will keep shutting down again.

Therefore, it is recommended you contact an HVAC technician to diagnose the problem and give you the solution. You also need to check if you need to replace any new parts if it’s included in the product warranty.

You can contact the contractor company who install the furnace since they will be familiar with the product and installation. However, if you don’t know the contractor company who install the furnace, you can contact another HVAC technician but make sure that they are certified and licensed.

If you want to have several quotations of the furnace repairs, it is suggested that you go to the website where they could compile quotations from several furnace repair companies, and you can select one from the recommendation list. Check not only price but also the review and record when you choose the repair company.

Cost of Furnace Flame Sensor Replacement

If the problem occurs because of the flame sensor is dirty and you can clean it by yourself, you will spend less than US$ 5 because you will need only for an emery cloth and your skill. If the flame sensor needs to be replaced, the cost varies from US$6 to US$ 75. It will be based on the model of the furnace and if the furnace brand can use a universal part or need to buy an OEM part. Most of the flame sensors cost no more than U$40.

However, if you have already cleaned the flame sensor and it still doesn’t work and you prefer to have an HVAC technician to replace it, you will need to pay a minimum service fee and the cost of a new flame sensor part. A minimum service fee will cost from US$ 65 up to US$150. If the furnace flame sensor needs to be cleaned only, then you just need to pay the minimum service fee only.

But if the furnace flame sensor needs to be replaced, you will need to pay the minimum service fee and additional cost to replace the flame sensor which will be around US$ 6 to US$75 depends on the brand and model.