Skip to Content

Ecobee Furnace Not Lighting? Here’s Why!

Your furnace depends on a continuous flame to ensure heated air can be distributed throughout your home. If your furnace isn’t lighting even after setting your Ecobee to heat, it means no heat is being produced, leaving you and your family cold during the winter months. So, what’s causing this unusual issue, and is there a way to fix it?

Your furnace isn’t lighting with the Ecobee because the pilot light isn’t lit, the ignition sensor is dirty or faulty, or the gas valve is closed. You can get the furnace to light again by relighting the pilot light, cleaning or replacing the ignition sensor, and opening the gas valve.

This article will help you understand why your furnace with the Ecobee isn’t lighting. We’ll then go over how to fix each problem. 

Unlit Pilot Light

Before diagnosing the issue, consider the age of your furnace. You may not realize it, but the model and age do make a difference in the problem. 

Namely, if your house is equipped with an older furnace, it likely uses a pilot light. Modern models have moved to an electrical ignition system. 

If your furnace has a pilot light, it needs to be lit to ignite the gas. So, it’s a good idea to check if the pilot light has gone out. When the pilot light isn’t lit, the furnace in your home can’t ignite the burners. In turn, no heat can be produced, and your home will run cold. You won’t see any flames in the burner regardless of your settings on the Ecobee thermostat. 

How To Fix

First, determine whether your furnace uses a pilot light or an electrical ignitor. If you’re not sure, you can visually inspect the furnace. Even better, consult the owner’s manual or the technical specifications of the furnace.

Here’s what you need to do if your furnace uses a pilot light:

  1. Turn off the furnace.
  2. Open the combustion chamber.
  3. See If the pilot light is lit. You may be able to see the flame without opening up the entire furnace. 
  4. If no flame is present, you need to ignite the pilot light manually. 
  5. When lighting the pilot light, make sure you use a long tip lighter. The pilot light is a bit out of reach, so you need the extra length to reach it.

If you simply need to ignite the pilot light to get rid of the problem, follow the instructions laid out in the video below:

Dirty Ignition Sensor

If your furnace uses a modern ignition system, it has a few additional parts. In addition to an electric ignitor, your furnace also houses an ignition sensor on the inside. This is sometimes called the flame sensor. 

The sensor detects a flame in the burner. It is inserted into the combustion chamber and regulates the opening and closing of the gas valve. Due to its position, the sensor is susceptible to dirt from combustion gases and particles that enter the furnace. 

When dirt and debris collect on the sensor, it becomes less efficient. Eventually, the sensor won’t detect a flame at all, causing it to close the gas valve. When this happens, your furnace can’t light. 

How To Fix

If you haven’t had your furnace serviced recently, it’s time to get into the furnace and clean the sensor:

  1. Turn off the furnace.
  2. Open the main compartment.
  3. Locate the flame sensor. The sensor is attached to a metal rod that sticks into a hole in the combustion chamber. 
  4. Remove the flame sensor carefully. Make sure to loosen any screws keeping it in place. 
  5. Once removed, use fine sandpaper to clean the part. A can of compressed air will help you get rid of any small grains left on the sensor. 
  6. Return the sensor to its original position and fasten it properly before turning the furnace on. 

Watch the following video if you need help cleaning the flame sensor:

Faulty Ignition Sensor 

Sometimes, debris builds up on the flame sensor and causes problems with the ignition process. Then there are times when the sensor itself becomes damaged or faulty. 

You should understand how to differentiate between a dirty and a broken flame sensor. 

If the flame sensor is broken, no cleaning will restore its functionality. 

You can inspect the sensor for damage while you clean it. This way, you don’t have to remove it from the furnace twice.

After cleaning the sensor, it should be easier to see if there are cracks or chips.

How To Fix

If you find signs of damage on the flame sensor, there is only one fix — replacing the flame sensor. 

The sensor is a relatively small and inexpensive part, but you need to make sure it’s compatible. Here’s how to replace it:

  1. Open the furnace.
  2. Open the main compartment.
  3. Remove the flame sensor from the furnace and take it with you when buying a replacement part. Ask the shop assistant for help to ensure it’ll fit into your furnace. If you’re buying online, make sure it’s compatible with your furnace model.
  4. Install the new sensor onto the furnace rod and put it back into the furnace.
  5. Close the furnace door before turning the system back on.

Here’s a video that shows you how to replace the flame sensor:

Closed Gas Valve

Another thing you want to check is the gas valve. The gas valve is responsible for controlling gas in the furnace.

The gas valve is automatically opened and closed by the flame sensor. Most gas valves also have a manual switch. If this switch is closed, gas won’t come through the valve, even when the furnace calls for gas.

How To Fix

You need to inspect the gas valve to see if the switch is closed:

  1. Turn off the furnace.
  2. Find the gas valve. If you don’t know where it is, find the line that runs from the gas supply toward the furnace. Follow this into the furnace until you find a box. 
  3. Check for a small switch on the flame sensor. See what position it’s set to. 
  4. If the switch is closed, flip it open.
  5. You should also check the gas line to ensure nothing is blocking it.


A failing pilot light or ignition sensor can cause your furnace not to light. In some cases, the cause may lie with the gas supply instead. Understanding the potential reasons for the issue is the first step to finding a fix.


  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

As an Amazon Associate, we earn from qualifying purchases. We may also earn commissions if you purchase products from other retailers after clicking on a link from our site.