October 5, 2023
Why won’t my furnace turn on?

Most people take a working furnace for granted, assuming it’s going to turn on when it’s cold outside to keep their home warm. That’s part of why you may experience stress when it fails to start properly. Discover six common reasons your furnace may fail to turn on and what you can do to fix it.

1. Ignition Problems

If you have a fuel-burning furnace, such as one that uses gas or propane, you’re going to have some kind of internal ignition mechanism. On older models, this may be a standing pilot light. On newer models, you may have an intermittent pilot or an electric ignition system, such as a hot surface igniter.

If your furnace has a standing pilot light, it may have blown out. This can happen for a variety of reasons, including a strong enough wind outside. The easiest way to see if you have a standing pilot is to check your owner’s manual. This will also contain the instructions on how to relight it. Additionally, you may find instructions on a label on the side of the furnace.

In the event you have a newer furnace with a hot surface igniter or an intermittent pilot, you might need a part to be replaced. Intermittent pilots use an electric spark igniter to light the pilot when it’s time for a heating cycle. Hot surface igniters use electricity across a ceramic surface to create enough heat to ignite the fuel. It’s not uncommon for hot surface igniters to wear out and need replacing before the end of your furnace’s service life.

2. Airflow Problems

Airflow plays a critical role for your furnace, not only for heating the air in your home but also for burning the fuel. Without the proper airflow, your furnace will snuff out and possibly become completely unable to turn on. Lack of proper airflow can also cause the system to overheat, damaging the heat exchanger.

Airflow problems can be as simple as a clogged air filter. Look at your filter and change it if it’s visibly dirty.

Your furnace may have an induction fan to help draw air through the burn chamber and out through the flue. Your furnace won’t light and cycle if this isn’t working properly.

Finally, the circulating fan may be malfunctioning. If the circulating fan fails to start, your system will overheat and shut down. If you suspect a fan isn’t working, call for a technician to troubleshoot the issue.

3. Electric Problems

Your system also relies on electricity to run various components, including the control board. If there’s a problem with the electricity supply to the system, it won’t run.

Start by checking the shutoff switch on the side of the unit and make sure that it’s in the On position. If it is, check your system’s breaker on the breaker panel. This can sometimes trip as a result of incidents from a strong thunderstorm to a failing circulating fan.

If your circuit breaker continues to trip, schedule an HVAC technician to investigate. A tripped breaker signals that there’s an overdraw on the system. If you ignore the issue, you risk damage to your furnace. Some electric problems may require the help of a professional electrician alongside your furnace technician, as they can also present fire hazards.

4. Thermostat Problems

Your thermostat is the brain of the heating system and can cause the system to fail to start. Begin by looking at the thermostat to ensure that it has power.

Next, check the thermostat settings. Ensure it’s set to heat and the fan is set to Auto. Check to ensure the time on the thermostat is set accurately, then check the thermostat programs. Check both the temperature settings and the times of those settings to ensure it’s changing when you expect it to.

It could also be that your thermostat is nearing the end of its service life. Digital thermostats have an expected life of 10 to 15 years, after which the sensors will stop functioning as accurately. If your thermostat is more than 10 years old, you may want to consider replacing it with a new one.

5. Sensor Problems

Your furnace has several sensors built in that work as safeguards to keep it safe while running. However, over time these sensors may not work as well, which can prevent the system from working properly.

One of the most common sensors to go bad with aging systems is the upper limit switch. This measures the unit’s temperature and shuts it down when it gets too hot in the furnace’s plenum. As the system ages, this may not work as well either due to wear or simply because the flame sensor rod becomes dirty. This may cause it to trip early, shutting down the system prematurely or preventing it from heating to the right temperature to begin with.

There’s also a flame sensor in the burn chamber that ensures there’s a flame burning when the gas is flowing. If the sensor doesn’t detect a flame, it will kill the gas supply, preventing a dangerous fuel buildup in the chamber. Over time, the flame sensor gets dirty with byproducts from the burning fuel. This is why your maintenance technician includes cleaning the sensor as part of your routine furnace maintenance.

6. Fuel Problems

Without the proper fuel supply, your furnace won’t turn on. If you can’t find any other probable cause of your furnace problems, you may want to investigate a fuel issue. Start by checking the fuel shutoff valve near your furnace and ensure that it’s in the On position. If you had furnace work done recently before the start of the season, your technician may have failed to turn it back on.

If the shutoff valve to the furnace is on, check any other appliances you have that run on the same fuel supply, such as your water heater or stove. If they aren’t turning on either, you could have a master supply issue to your home. Check the master shutoff valve, which is usually outside your home. If this is on, you may need to contact your utility company to have them investigate the issue.

There could be issues outside of the fuel shutoff switch preventing fuel from arriving inside the furnace. We’ve already discussed sensor issues that could prevent the regulator from opening. However, you could also have a problem with the fuel regulator itself. A technician will check the regulator during maintenance to ensure the right pressure of fuel arrives at the burner. Turn to us for heating repair!

People around Selma who want reliable heating and cooling services turn to the experts at Beyer Air Conditioning & Heating. Our team takes pride in providing AC and heating repair, maintenance and installation together with indoor air quality solutions and duct cleaning. Call to schedule your furnace repair appointment with one of our trusted technicians today.

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