smart thermostat calgary

When your thermostat says heat on but furnace not running, it’s more than a mere inconvenience, especially during the colder months. Such a situation not only leaves you shivering and cold, but it also makes you puzzled and kind of frustrated.

This is why, understanding the complexities behind why a furnace may not run despite the thermostat’s signal requires diving into the details of home furnaces and systems that are involved in heating your home.

In this article, we’re exploring ways to diagnose, understand, and get the problem fixed, from simple DIY checks to situations that could need professional help.

But first, what does your Heating System consist of?

The thermostat, a central control unit, is the brains of your heating system. Depending on the desired temperature and settings you’ve selected, it will send signals to the furnace to begin or halt the heating cycle. From the most basic models that only control the temperature, to the most advanced “smart” thermostats that can learn your routine and preferences and adapt their settings accordingly, there is a wide range of options available today.

The furnace is the main component of your heating system; it is the one that produces the hot air that warms your house. To work, it takes chilly air from your home, filters it, and then uses a heat exchanger to warm it. The ducts then return the heated air to your home.

Each of the four main fuels used to power furnaces—electricity, natural gas, oil, or propane—has its own specific way of producing heat. As an example, electric furnaces employ heating components powered by electricity, while gas furnaces use burners powered by natural gas.
Furnace picture

Furnace Fan (Blower): The blower, or furnace fan, is responsible for distributing the hot air in your home once it has been heated by the furnace. Your heating system’s efficiency and efficacy are enhanced by this essential component, which guarantees the uniform dispersion of warm air.

Heat Exchanger: This component is crucial for safety and efficiency. It’s a series of coils or tubes that gets heated up by the furnace burner (in the case of a gas furnace) or heating elements (in an electric furnace).

The air from your home passes over these hot surfaces, warming up before being circulated back into the rooms. The design of the heat exchanger prevents combustion gases from mixing with the circulating air, ensuring that only clean, warm air is distributed.

Blower Motor: The blower motor is responsible for turning the fan on your furnace and circulating air throughout your home. This motor’s speed controls the airflow, which in turn affects the heating effectiveness and noise level of the furnace, depending on your system.

Fan Limit Switch: The fan limit switch is a safety feature that regulates the blower motor based on the internal furnace temperature. It checks the air temperature and turns on the furnace fan only when it’s safe to do so. The device stops the fan from releasing chilly air at the beginning of the heating cycle and keeps it running until the leftover heat is used up after the burner turns off.

Electronic Ignition or Pilot Light: The gas furnace’s ignition system is responsible for starting the heating process by igniting the fuel. Modern furnaces typically employ electronic ignition systems that only turn on the burner when the heating cycle starts, which greatly improves efficiency compared to older types that may use a pilot light that burns continually.

Common Reasons for the Discrepancy

When problems arise with your heating system, you should usually check the thermostat first because it is the main point of contact between you and the system.

  • Batteries: Although it may sound obvious, a thermostat's inability to communicate with the furnace could be caused by dead batteries. To keep your heating system running smoothly and without interruptions, check and replace these batteries regularly.

  • Settings: Incorrect settings are another possible cause. Importantly, make sure the thermostat is in the "heat" position and that the intended temperature is higher than the room temperature right now. Problems can often be as easy as a user inadvertently changing the settings or turning the mode to "off" or "cool."

  • Malfunctioning Thermostat: A broken thermostat might be the result of a number of factors, including the passage of time, dust buildup, improper wiring, or other electrical problems. For your furnace to begin heating, a properly operating thermostat must be able to transmit the appropriate signal.

    Sometimes cleaning the thermostat's internal components or recalibrating it might fix the problem, but for older versions, it could be essential to replace it.

After checking that the thermostat is functioning properly, you should look into any problems that may be affecting the furnace.

  • Circuit Breaker and Power Supply: A blown fuse or a tripped circuit breaker is a typical cause of a furnace not operating. You can easily check this on the electricity panel in your home. It is also important to turn on the furnace's power switch.

  • Air Filters: To keep a furnace running smoothly, air filters are essential. Overheating and subsequent automatic shutdown of the furnace might occur if the air filter is dirty or blocked, restricting the airflow. An easy preventative measure to take is to check and replace the air filter regularly.

  • Fan Limit Switch: Until the air inside the furnace reaches the proper temperature for circulation, the fan will not turn on thanks to the fan limit switch. If it's malfunctioning, the fan won't turn on, and the heating won't continue. In most cases, a specialist is needed to diagnose and replace a fan limit switch that is not working properly.

  • Heat Exchanger and Blower Motor Issues: When it comes to heat exchangers and blower motors, problems might get trickier. After the air has been heated by the heat exchanger, it is blown all throughout your house by the blower motor. If your furnace experiences problems with these parts, it might drastically reduce its heating capacity and should be serviced by a professional.

  • Pilot Light and Electronic Ignition: The ignition system is crucial for gas furnaces. The furnace may not turn on due to a pilot light that has gone out or an electrical ignition that is malfunctioning. Sometimes all it takes to remedy the problem is to relight the pilot light, but if it keeps happening, it could be time to call an expert.

The heating cycle can be interrupted by electrical issues, such as broken wiring in the furnace or between the furnace and the thermostat. Due to the complexity and potential dangers of electrical repairs, these tasks are best left to trained experts.

Certain furnace problems, particularly those related to the furnace's internal components like the fan motor, blower motor, heat exchanger, or intricate electrical issues, demand the expertise of a professional HVAC technician. Not only can they safely diagnose, correct, and fix these problems, but regular maintenance visits can also prevent them from occurring in the first place.

Troubleshooting Steps

  • Thoroughly Check Thermostat Settings: Start by verifying that your thermostat is indeed set to the “heat” mode and that the temperature setting is higher than the current room temperature. It’s a common oversight that can easily be rectified and is a crucial first step in troubleshooting.
  • Replace Thermostat Batteries: If your thermostat runs on batteries, you might want to check if the batteries are weak or dead. If so, you may need to replace the batteries. If they are faulty, replacing them should fix the problem by allowing the thermostat and furnace to communicate properly again.
  • Inspect the Circuit Breaker and Furnace Switch: There are instances when the answer is as simple as checking the power switch on the furnace or the circuit breaker. It is possible to turn off the furnace by inadvertently turning off the power or by tripping the breaker. Maybe turning the furnace switch back on or resetting the breaker may fix it.
  • Check and Replace the Air Filters: If the air filters are dirty or clogged, airflow is restricted, which can cause the furnace to overheat and shut off automatically as a safety measure. Unrestricted airflow and the avoidance of unanticipated furnace downtime are both guaranteed by routinely checking and replacing these filters.
  • Reset the Furnace: The built-in reset button on many furnaces allows you to restart the system and eliminate any minor technological faults. Follow the on-screen prompts to locate and push this button. If your heater stops working, try this easy fix.
  • Verify the Pilot Light or Electronic Ignition: When using a gas furnace, make sure the pilot light is lit or that the electronic ignition is working properly. Failed ignition could cause the furnace to not start. An important part of diagnosing the problem is making sure the electronic ignition system is working or that the pilot light is on.
  • Examine the Fan Limit Switch: This essential safety feature regulates the furnace fan so that it turns on only when the air gets hot enough. If this switch fails, the fan, and by extension, the furnace, could not turn on. It typically takes a skilled HVAC technician with extensive knowledge of furnace operations and a deeper understanding of this component to adjust or diagnose it.
  • To find out why your furnace isn’t turning on when the thermostat says it should try these troubleshooting procedures. Some issues may just require a little tweaking, while others may be signs that you should call in the pros.

How to prevent this issue from happening?

Let’s look at the essential steps to help prevent common furnace issues, incorporating well-known thermostat brands like Nest, Honeywell, and Ecobee, which play pivotal roles in your heating system’s functionality and efficiency.

  • Utilize the Nest app to monitor your energy consumption patterns and adjust your heating schedules to optimize efficiency.
  • Pay attention to maintenance alerts from your Nest thermostat. Regularly changing your air filters based on these reminders can prevent furnace strain.
  • Use the Nest thermostat's feature to check your furnace's usage history. This can help identify unusual patterns that might indicate a need for maintenance or inspection.
  • Set up regular maintenance reminders through the Honeywell Home app, ensuring you never miss a furnace filter replacement or annual inspection.
  • Utilize the adaptive recovery feature, which learns how long it takes to reach desired temperatures at different times, thereby minimizing the amount of time your furnace needs to work hard.
  • Monitor the indoor air quality reports available through some Honeywell models to adjust your heating needs and filter changes accordingly.
  • Take advantage of the Ecobee app’s insights and reports to track your heating system's performance over time. Sudden changes in energy use can indicate a need for furnace maintenance or filter replacement.
  • Set up ecobee to send alerts for irregularities in your heating system's performance or when it’s time to replace your air filters.
  • Use the voice control feature to set reminders for checking and sealing ductwork or inspecting the furnace for any signs of wear and tear.


When faced with a scenario where your thermostat signals “heat on” but the furnace does not run, understanding the potential causes and knowing how to troubleshoot can save you time and discomfort. From checking simple issues like thermostat settings and batteries to more complex furnace components, a step-by-step approach can often resolve the problem.

However, recognizing when to call in professional help is equally important to ensure your heating system operates safely and efficiently. Regular maintenance and awareness of your heating system and thermostat’s batteries and components can also prevent future issues, keeping your home warm and comfortable throughout the colder months.

If you wish to get a professional HVAC technician for the diagnosis of your heating, air conditioning, or any other service, Comfort Union can be the right partner for you. Visit our website to know more!

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Various types of heating and air conditioning equipment: furnaces, heat pumps, air conditioners, and ductless mini-split systems.
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