Second Stage Heating Not Working: Reasons and Solutions!

Second Stage Heating Not Working: Reasons and Solutions!

Having a well working heating system is essential for staying warm and comfortable on extreme cold days. But if you find out that your heating system is not working, it can be a frustrating and worrisome situation. 

So, what would be the reasons behind your second stage heating not working

Your second stage heating won’t work because of the thermostat issue, air filter issue, dirty flame sensor, lack of maintenance, and because of a dead blower capacitor. Also, wiring damage or problems with malfunctioning wiring can be an issue. You can solve this problem by maintaining it regularly and checking the wiring connection in your system.

Let’s first talk in detail about the major and common  problems for second stage heating not working and as well as possible fixes.

5  Common  Reasons  Behind  Your  Second  Stage  Heater  Not  Working: Quick Overview

Your second stage is not working and the problem can be difficult to solve as there are many reasons behind it.  

Let’s check the common reasons in the table below. Take a look!

Reasons  Solutions 
Faulty thermostat and wiring Check the auto mode is off, clean the dirt from the thermostat, unlock the device from settings. Check the wirings properly and replace if damaged or frayed
Dead blower capacitor You have to change the damaged capacitor.
Furnace limit switch  Check the limit switch’s working and reset it if required.  
Chimney exhaust flue Clear all the debris and duct from the chimney and set it back again.
Lack of maintenance Clean the blower motor, air filter and flame sensor. 

Now, let’s get into the depth of the reasons and solutions and troubleshoot your second stage heating as we did with the Burnham boiler troubleshooting. And do check if your furnace has this problem or not.

Note: Turn your furnace’s power off before attempting any troubleshooting.

Reason 1: Faulty  Thermostat  And  Wirings

Well, Thermostat itself can be the cause of your heater’s problem. Because it’s responsible for controlling the temperature and ensuring you’re comfortable all year around. Here are Some common issues with the thermostat. 

01. Auto mode on:

Thermostats occasionally may not allow manual temperature adjustment, when it’s set on auto mode. So, then your thermostat won’t pick your command. 

Solution: You need to change your thermostat’s auto mode and turn the heat mode on. 

02. Sensor malfunction: 

A sensor problem is probably to blame if your thermostat displays incorrect settings. 

Solution: You can compare the reading of your thermostat with a room thermometer. In this case, you may need to seek help from an HVAC professional. Because, fixing this issue by yourself can be difficult. 

03. Dirty Thermostat:

The delicate thermostat components can become clogged with dirt and debris. This can block the sensor and lead to incorrect temperature reading. 

Solution: you need to clean your thermostat with a soft cloth or brush. Note  that you can’t use any wet cloth or wipe for this cleaning, as it may cause the internal components damage of your thermostat. 

04. Lock on the thermostat: 

Smart thermostats offer lock or range control functions to stop unauthorised temperature changes. Sometimes you may turn the mode on and forget. 

Solution: you need to check the settings of your thermostat device and unlock it if required. 

Before starting the faulty thermostat wiring in detail, let’s just check the table below. If you have a smart thermostat ecobee or nest, then this part is definitely for you.

Thermostat  Problems Solutions
Ecobee thermostat  Not connected W2 wire to furnace W2 terminal or damaged wire.  Connect the ecobee W2  and check the wire, if it is damaged then change or fix it.
Nest thermostat  Disconnection of W2 wire from the furnace or damaged, leak wire.  Check the wire’s condition and fix or change if it is defective or damaged. Connect the furnace W2 terminal to your nest W2 wire. 


Connection  Of  Thermostat  And  Furnace:

Connection  Of  Thermostat  And  Furnace

Source: Twitter

For second stage heating not working, the main concern is the wiring connection between thermostat and furnace. If the thermostat is not connected to the furnace  correctly, it may not be sending the signal to activate the second stage heating. 

The W2 wire of your thermostat and W2 terminal of your furnace terminal board  controls the second stage heating process. Hence, for the second stage heating, the connection between the W2 wire and the W2 terminal should be maintained.

For better understanding, here are two videos that you can check to connect the wires. 

1: Nest thermostat: 2 Stage Thermostat Wiring For Nest

2: Ecobee thermostat: 2 Stage Heating – Ecobee Thermostat Wiring 

If you have two stages of AUX heat, you will connect AUX2 to W2 terminal on your thermostat to connect the second stage. If the wirings are okay it there might be a problems with the relay switch, many people have problems with taco SR relays.

Note: Always ensure that your system is powered off before performing any modifications to your system.

Reason 3: Dead  Blower  Capacitor 

Dead Blower Capacitor

Source: IFIXIT

Have you ever taken a look at your blower capacitor? It usually looks like a large battery.

Capacitors have tolerance levels that determine their performance. If the tolerance level drops below a certain point, it can impact the RPM (revolutions per minute) of your blower, preventing it from reaching the desired speed. At times, the capacitor may even fail to activate the blower altogether. 


You need to repair the blower capacitor or change it. Changing the capacitor will be a good option. Let’s check the steps below of changing the capacitor of your furnace. Before jumping into it, you need precaution and some tools.


  1. Socket wrench or screwdriver 
  2. Adjustable wrench 
  3. Gloves

Step 1: First, turn the power off of your furnace.

Step 2: Remove the top cover panel using the socket wrench if required. If you have a push lock on your furnace, just simply unlock it and remove the cover.

Step 3: Remove the blower cover panel with a socket wrench or screwdriver if needed.

Step 4: If you have the control board in front of your blower, first remove this. You can take a picture of the wiring connection, it may help when you reconnect it.

Step 5: Disconnect the motor wires. Unscrew and set the control board off to the side. 

Step 6: Find the capacitor and always assume capacitors are charged, as there is a risk of a serious electrical shock. You can place a resistor or a screwdriver with an insulated handle across each terminal. This will short out and discharge the capacitor.

Step 7: Now disconnect the wires and remove the capacitor. 

Step 8: You will see the rating of how much energy can be stored in the capacitor is written over the capacitor. This should be matched exactly with the new one. You will also see the voltage rating written there. You can use a capacitor with an equal or higher voltage rating but never with a lower rating. 

Step 9: Connect the wires just like before and attach the capacitor with the screwdriver again. 

Step 10: The last step is to reattach and reconnect all together to set them as the way you remove them. 

For you better understanding, you can also check the video 

Reason 4: The  Furnace  Limit  Switch  

A safety switch that recognizes when the furnace is overheating is the furnace limit switch. The second stage heating might not function if it is tripped. 


Check the switch if it is running over or not and if required reset it. Let’s jump into the process of resetting it by yourself. 


  1. Screwdriver.
Furnace Limit Switch

Source: Inspecta Pedia

Step 1: Find the location of the heating duct in your furnace. The vent is typically found in the basement of the home. The panel will be located underneath the duct. You can open the panel with a screwdriver. 

Step 2: you need to search the white limit switch. You may find It at the top of the panel. The limit switch will be surrounded with a white or silver cover, depending on your furnace model. You need to remove this. Then, you will find the body of the switch with two metal arms. 

Step 3: look at each arm to identify the settings. Furnace’s low and high temperature is controlled by these two arms. 

Step 4: Identify the component located in the middle of the two arms, which controls the furnace’s fan. 

Step 5: Set the temperatures in the middle component to 105-115 degrees fahrenheit. 

Step 6: Set the temperature on the left component to 90 degrees fahrenheit. 

Step 7: Set the right arm to 200 degrees. 

Step 8: Now pull out the white/ silver switch to set the furnace to the automatic mode. Not to push it in, all your settings will be cleared.

Step 9: Close the panel with the screwdriver. 

By these steps above, I hope you can replace your furnace limit switch successfully. 

Reason 5: Chimney  Flue  Exhaust 

Sometimes birds may fall into the chimney. To check this, turn the thermostat and the furnace off. For this issue, your whole heating system may not work including the second stage. 


You can clean your chimney with some tools and need precautions. 


  1. Chimney sweep brush (according to the size of your chimney, you will have a round or square in shape.)
  2. Flexible chimney cleaning rod.


  1. Wear a mask and hand gloves for protection.

Reason 6: Clogged Air Filter

Clogged Air Filter

Source:Hydes AC

During the winter, the most common reason for service calls is a lack of maintenance. It’s the most likely cause of your heat not working properly. A clogged blower motor can cause equipment failure. If there is not enough cold air flowing over the heat exchanger to prevent it from overheating, it will not work.

When the motor is unclean, the heat exchanger is not exposed to enough flowing air. That could be why your second heat unit isn’t producing enough heat to keep the house warmer. 

A clogged air filter may limit airflow and trigger the furnace’s second stage heating shut-off. It can also cause problems like the heater being stuck in standby mode.

the flame sensor will not “sense” the flame, if it’s dirty and it will turn off as soon as it is turned on. 


Clean your blower motor when you will find it clogged. Secondly, Change your air filter every three months. And the flame sensor should also be cleaned frequently. So, these are the causes and fixes that you can check and resolve by yourself.

How Do You Factory Reset A Second Stage Heater?

If the above solutions are not enough to solve your problem of second stage heating, then you should perform a factory reset. There are many ways to reset a second stage heater but we’ll talk about the most common and easy one. 

Let’s move on to the step by step guidance of resetting your heater – 

Tools Needed:

  • Screwdriver.
  • Hand gloves.

Step 1 : Cutting The Power And Removing The Panel 

Find the furnace power switch near the furnace and turn it off. If you can’t find the switch, simply turn off the furnace’s main circuit breaker. 

Step 2 : Press The Furnace’s Reset Button

You need to open the metal housing of the blower compartment with the help of a screwdriver. Before opening the blower compartment, make sure the furnace is turned off.

They typically have a yellow or red tint. The area of the reset button varies. depending on type, however, you may find it inside the blower unit.

Once, press the reset button. Reconnect the furnace’s power. If it does not return, your furnace has a safety problem and needs a repair. 

Step 3 : Reset The Heat Pump 

Some heat pumps include two reset buttons: indoor unit and the outdoor unit. First, turn off the heat pump and then, press both reset buttons at the same time.

If your heat pump doesn’t have a reset button, it will have a power switch. After switching it off, wait a few minutes, then flip it back on.

Step 4 : Reset The Circuit Breaker

Try resetting the circuit breaker if the previous methods haven’t made your furnace or heat pump work. By using the power switch, turn off the furnace or heat pump.

Find the heater’s breakers. Heat pumps often use two breakers. One is for the air handler, and the other is for the outdoor unit. turn them both off, wait one or two minutes and then turn them both back on. Lastly, Turn on the power switch for your heater.

Congratulations! You have successfully performed a factory reset of your second stage heating system. Now check and verify whether it’s working or not. 

Frequently Asked Questions (FAQs):

How Does Two Stage Heating Work?

Two-stage heating works by two levels of heat output: high for cold winter days and low for milder days. A two-stage device runs longer and distributes heat more evenly because the low setting is sufficient to meet family heating needs 80% of the time.

Is  Two-stage  Heating  Worth  It?

The two-stage furnace is more efficient than the one-stage because it doesn’t release as much fuel into the heat exchanger when the home is only somewhat cold. If it’s 5 to 10 degrees outside, a two-stage furnace will run in the partially-open position and only use 70% of the energy it normally would.

Do I Need A Special Thermostat?

No, you don’t need a special thermostat for the two stage furnace. A control board of a two-stage furnace is always programmable to use a single or two-stage thermostat. If you are using a single stage thermostat, the control board controls the second stage.


Thank you for being patient till now. I tried to resolve your issues regarding second stage heating not working. Hope, it will work for you. Different types of heating systems have different problems with second stage heating in this case. If required, you may seek help from an HVAC professional.

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