Why Your Furnace Won’t Stay On? Common Reasons For Failure

Funace wont stay on

If you live in or around Raleigh or Garner, you know that we can sometimes get hit hard with cold weather here in North Carolina. As a result, it is imperative that your heating system works properly during a cold winter day or night when there are extreme temperatures.

If you are having issues with your furnace staying lit, our Bowman Mechanical Services experts in furnace malfunction issues are here to help you figure out why.

There are a lot of potential warning signs to diagnose why your furnace turns off- from minor issues like the buildup of dirt and debris to more severe safety concerns like issues with the gas line, it is important to have an HVAC furnace professional come to inspect and repair your system.

How Furnace Ignition Systems Work

Not all gas furnaces necessarily work exactly the same but for the most part, an average furnace ignition heating system will operate in a particular sequence.

Here’s how most furnaces operate in order to ignite:

  1. The thermostat signals for heat as a result of colder temps.
  2. The draft inducer motor starts to circulate fresh air, which is an important safety feature for the combustion chamber.
  3. The gas valve opens, transferring gas to the pilot burner. *If you have a direct ignition furnace, your furnace does not have a pilot light, but a flame sensor.
  4. An electrical spark ignites, turning the pilot light on. *Furnaces with a standing pilot light it must be lit directly by you in order to turn on.
  5. If the pilot light was lit successfully, the flame sensor alerts the furnace.
  6. Gas is transferred through the gas valves to the main burners of the furnace.

When gas is involved in the heating cycle, the safety concerns are significant, and the well-being of the members of your household is the priority. We suggest having an HVAC pro perform annual maintenance and prevention services on your old furnace to reduce the possibility of furnace problems.

However, if it’s too late and an issue is already occurring, restricting your furnace from operating correctly, it is important that you schedule a furnace repair as soon as possible.

What Commonly Goes Wrong With A Gas Furnace

Some of the common issues that cause gas furnaces to stop working or need repairs are:

  • Due to age your old furnace no longer operates.
  • The furnace is not the right size for your home.
  • Overheating because the heat exchanger gets too hot.
  • Insufficient airflow or insufficient gas pressure.
  • A defective, malfunctioning ignition board, flame sensor, light switch, thermostat, thermocouple, fan limiter, or draft inducer fan.
  • The drainage line is blocked, resulting in a full condensate pan.
  • Temperatures are so low that the furnace cannot stay lit.

Flame Sensor Is Triggered

The purpose of the flame sensor is to be certain the gas valve opens only when flames are burning. If the gas valve is open when the furnace is not lit, it could result in toxic gas buildup. This is extremely dangerous and can lead to a gas leak, fire, or gas explosion. While this sounds very scary, there are luckily warning signs before the worst-case scenario occurs.

Signs of gas accumulation in the valves due to a triggered flame sensor are:

  • Water leaks that puddle around the surface of the furnace.
  • The appearance of a yellow burner flame can be a sign that carbon monoxide is not filtering out of the system properly.
  • Rusted, corroded flue lines indicate CO gas is not properly filtering out of the system.
  • Your furnace’s old age is impacting the flame sensor operating in the right way.
  • High utility bills can often mean that you simply need an air filter replaced, but in more extreme circumstances with gas furnaces, unexpected increases in energy costs can also mean that the flame sensor is making it difficult for your heating system to work.

If you are worried you may be experiencing trouble with your flame sensor or that there is insufficient gas flow, your system needs to be inspected and repaired by a furnace burner expert.

The Thermostat Is Malfunctioning

Your thermostat is responsible for telling the furnace when to turn on and off, based on the temperatures in your home. If your thermostat is malfunctioning, that lack of communication with the heating system results in your furnace not knowing when to light.

If the thermostat is not operating properly, it can send the wrong signals to your furnace at the wrong times, resulting in an overheating furnace or other heating system problems.

How To Fix A Malfunctioning Thermostat?

A simple fix for a malfunctioning thermostat is to buy a new thermostat, and hopefully, the equipment will communicate with your gas furnace to reach the desired temperature. In case there is a more advanced issue, calling an HVAC pro is always your best solution to fixing a bad thermostat and helping it function properly.

Your Furnace Has A Defective Draft Inducer Motor

A draft inducer fan vents out any gases from the combustion chamber. The motor then continues to circulate oxygen to the furnace burner.

When the draft inducer motor is not working correctly, the pressure switch that measures airflow will not detect the flow of air at the correct rate, causing the heat exchanger to close. In contrast, it’s possible for the pressure switch to affect air circulation by not allowing the heat exchanger to close at all.

Older gas furnaces do not all have draft inducer motors, but most newer furnace heating systems will.

How To Fix A Defective Draft Inducer Motor?

Most draft inducer designs are complicated and unless you are an HVAC pro professionally trained to repair furnace system parts like a blower motor, pressure switch, and draft fans you can ultimately end up making the system worse overall. When dealing with gas furnace motors and switches, we always recommend leaving system repairs to professionals.

Your Furnace Has A Dirty Flame Sensor

One of the most common issues with malfunctioning gas furnace systems is a dirty flame sensor. The easiest way to diagnose this issue is to pay attention to the time frame between your furnace turning on and then off again. If your furnace turns on several times and, within seconds, turns back off that’s a clear sign that your home’s furnace issue is due to a dirty flame sensor.

An important safety measure to take is to install a flame sensor that is designed to turn off the gas valve when no flame is detected. A flame sensor with the safety feature of automatically turning off the flow of gas when the pilot light doesn’t lite can keep your home and family out of harm’s way.

How To Fix A Dirty Flame Sensor?

Cleaning the flame sensor is the only way to fix it when it’s dirty, but it is easier said than done. We recommend scheduling a service with our gas furnace experts rather than trying to clean it yourself.

If you do opt to try cleaning the flame sensor on your own, it’s vital you do it correctly. Here is the sequence of how to troubleshoot a flame sensor in need of cleaning:

  1. Turn your furnace off entirely.
  2. Access the flame sensor by opening the door to the combustion chamber.
  3. Remove the sensor and clean it off rust, dirt, and buildup with light-grit sandpaper, emery cloth, or steel wool.
  4. Replace the sensor.
  5. Test your system to see if the issue is resolved.

The Furnace’s Thermocouple Is Broken Or Malfunctioning

The thermocouple detects if the furnace pilot light is functioning properly. When the furnace’s pilot light is out, the thermocouple will prevent unburned gas from flowing through the valves by closing them. When the thermocouple is broken, the gas valves function abnormally, causing furnace issues.

How Can I Fix A Broken Thermocouple?

Not to sound repetitive, but we again would recommend leaving a malfunctioning thermocouple repair to someone with knowledge and experience in furnace repair.

We want our local homeowners to remain safe, and while it can be frustrating to not have your furnace turn on properly, particularly in the cold winter months, putting your household in danger of gas coming through the valve and starting a fire is not worth taking gas furnace issues into your own hands.

Heat Exchanger Is Broken

A faulty heat exchanger is one of the common culprits to not keeping your pilot light lit. Heat exchangers use a limit switch that shuts the furnace when it’s overheated. When the heat exchanger is broken, their job of detecting those heat temperature levels isn’t being performed, resulting in furnace overheating.

What Does A Broken Heat Exchanger Mean For My System?

When your heat exchanger is constantly overheating, it limits the venting of combustible gases. When those gases are not vented out of your system, they can potentially lead to gas leaks, catch fire, or explode.

You guessed it! You should absolutely have an HVAC pro come to your home to service your broken heat exchanger and eliminate any potential issues that can lead to expensive, harmful outcomes.

If Your Home Furnace Won’t Stay Lit, Contact Bowman Mechanical’s Repair Services Today

We believe that keeping your home safe is the top priority for our clients. If your home’s gas furnace pilot light won’t stay lit, do not make the mistake of taking it into your own hands. Instead, call our professional team of furnace technicians at Bowman Mechanical Services.

Our HVAC pros will inspect and troubleshoot your furnace, and get all the heating components working properly to keep you and your family safe and warm this winter.

Contact us at  919-772-2759 or fill out the form below to perform an annual maintenance or repair service to your home furnace.

  • This field is for validation purposes and should be left unchanged.