The freezing Wisconsin winters make it essential that your furnace works properly. Having your furnace suddenly fail to turn on can be incredibly frustrating and can lead to your home quickly becoming unbearably cold. If you ever find yourself in this situation, you will generally need to contact a furnace technician to diagnose and repair whatever the issue is. That being said, there are a few things that you can check first, as the problem may be something that you can easily take care of on your own. Let’s now take a look at the most common issues that can prevent a furnace from turning on and what can be done about them.

1. Interrupted Electrical Supply

All modern furnaces are designed with a safety feature known as a limit switch that should automatically shut the heating system down if there are any issues that could overload its electrical circuit and cause the breaker to trip. Nonetheless, the first thing you should do if your furnace won’t turn on is to check to make sure that the breaker isn’t tripped.

Even gas furnaces require electricity to power their control board, inducer fan and electronic igniter, and electricity is also required to power the blower that circulates air throughout the system. This means that your heating system won’t start if electricity isn’t flowing due to a tripped breaker or any other type of wiring or electrical issue.

If the breaker is tripped, try to reset it and see if this allows your furnace to start. If the breaker instantly trips again when your heating system attempts to start, it indicates that there is an electrical issue that is overloading the circuit.

2. No Gas Flow

Your furnace obviously also won’t be able to light if gas isn’t flowing to the unit. If you have any other gas-burning appliances, you should check to see if they are still working, as there is always a chance that the gas supply coming into your home is cut off for some reason. You should also make sure that your furnace’s main gas shut-off valve is fully open.

If gas is flowing to your other appliances and not your furnace, it usually means that the gas valve is broken and stuck shut. Luckily, replacing a broken or faulty gas valve is a fairly easy and inexpensive fix.

3. Malfunctioning Electronic Igniter or Pilot Light

Unless your furnace was installed before 2010, it most likely uses some type of electronic igniter instead of the traditional pilot light found on older units. Either way, your furnace won’t be able to start if the electronic igniter isn’t working or the pilot light is out. Both an electronic igniter and a pilot light can fail due to normal wear and tear or various other issues and may need to be replaced.

If you do have a pilot light, the very first thing to do is check to make sure it is still light. If you can’t get the pilot light to ignite or it won’t stay lit, then there is most likely an issue with the thermocouple, pilot gas tube or pilot control.

4. Faulty or Burnt-Out Inducer Motor

The very first thing you hear when your furnace turns on is the draft inducer start, and this happens around 30 seconds before the furnace actually lights. Burning gas produces carbon monoxide and other hot combustion fumes. The draft inducer draws these fumes out of the combustion chamber, through the heat exchanger and eventually out of the building via the exhaust flue. This is important both for safety reasons and to ensure that the furnace works properly.

These combustion fumes are inflammable and would starve the burners of oxygen if they remained within the combustion chamber. This, in turn, would result in the gas flowing out of the burners not combusting fully, which means the furnace would produce far less heat.

This issue is the reason that the draft inducer runs before the furnace lights as it ensures that there are no fumes remaining inside the unit. The inducer creates negative air pressure inside the furnace, and this then activates the unit’s pressure switch. The pressure switch is then what signals the gas valve to open so that the furnace can then light. If the inducer motor is worn out or not working for any reason, the pressure switch can’t activate and the furnace won’t start.

5. Faulty Pressure Switch

The pressure switch can sometimes fail to activate even when the inducer fan is working properly. The switch has a small suction tube that detects the pressure and causes it to activate, and this tube can sometimes break or come loose. The pressure switch itself can also fail or get stuck in the closed position. In either of these situations, the solution is to either repair or replace the pressure switch.

6. Broken or Dirty Flame Sensor

If your furnace uses an electronic igniter, then it also has a flame sensor that works to detect when the burners are lit. If the flame sensor is dirty or broken, it won’t be able to detect that the furnace is lit. If the flame sensor doesn’t detect the flames and activate within a few seconds, the gas valve will automatically close and the furnace will shut down immediately. This is one of the most common furnace issues and also one of the easiest ones to prevent. All it takes is having your furnace professionally maintained every year as the technician will both clean and inspect the flame sensor to ensure it works correctly.

7. Overheating

A furnace limit switch is designed to automatically shut your heating system down if either the furnace or the blower fan starts overheating. This usually occurs due to a clogged air filter or some other airflow issue, but overheating can also result if your furnace is too large. If your system ever does overheat, the limit switch will prevent the furnace from turning on again until it senses that the unit has sufficiently cooled. Depending on the model, your furnace may also not start again after overheating until it has been reset.

8. Thermostat Issues

There is also the possibility that some issue with your thermostat is what is preventing your furnace from starting. It could be that the thermostat batteries are low or that there is a wiring issue preventing the thermostat from signaling the furnace to run. Your furnace could also be faulty or not getting an accurate temperature reading and thus not signaling the furnace to run even though your house is cold.

Your Local Heating and Cooling Experts

At Healthy Home Heating & Cooling LLC, our technicians have years of experience repairing all types of furnace issues and can quickly determine why your unit isn’t working and how to fix it. We service and repair all makes and models of furnaces as well as air conditioners, heat pumps, boilers and ductless mini-splits. If you need to replace your current HVAC unit, we also specialize in heating and cooling installation. We also offer duct cleaning and install indoor air quality equipment that can help you to breathe more easily. Give us a call today to schedule any HVAC service in the De Pere area.

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