Finding that your furnace suddenly won’t light can be incredibly frustrating. When this happens, most people immediately contact an HVAC company to have their furnace repaired. While this is often necessary, there are also some situations when the issue is something that you can easily overcome on your own. There are many different issues that can prevent furnaces from igniting and what can be done to fix them.
1. Clogged Air Filter
Many people are surprised to learn that something as seemingly minor as a dirty air filter can cause major issues for a furnace and potentially prevent it from turning on. An HVAC air filter is designed to trap dust, hair, and debris to prevent them from being drawn into the system and damaging or gunking up the furnace or blower fan. As your heating system runs, the filter eventually becomes dirtier and dirtier to the point where it can become completely clogged if you don’t replace it regularly.
If the filter is clogged, little to no cold air will be drawn into the furnace. This issue means that the furnace won’t be able to disperse all of the heat it creates, which can result in the unit overheating. All furnaces have something known as a limit switch that constantly measures the temperature of the furnace and blower fan. If either component gets too hot, the limit switch automatically activates and shuts down the heating system. When this happens, your furnace won’t turn on again until the limit switch registers that everything has sufficiently cooled.
This is the easiest problem to check and also to fix. If your filter looks black or you haven’t replaced it for a few months, try replacing it and then wait for an hour or so to see if your furnace will now turn on. This problem is also easy to avoid by making sure to replace your filter every 30 to 90 days.
2. Pilot Light or Electronic Igniter Issues
Most furnaces now use some type of electronic igniter. If you have a much older furnace, it may instead use a standing pilot light for ignition. Both pilot lights and electronic igniters commonly fail as a result of their age, and this will prevent the furnace from igniting. Unfortunately, diagnosing a broken or malfunctioning electronic igniter is not something you can do on your own. Instead, you will need to have a furnace technician test the igniter and replace it if it is bad.
If your furnace does have a standing pilot light, you will want to make sure that it is lit and producing a strong, steady flame. If the pilot isn’t lit, you can try relighting it to see if your furnace will not light. If you can’t get the pilot to light or it won’t stay lit, it could be that the thermocouple is dirty, damaged, or broken. Another possibility is that the pilot gas tube is clogged and preventing gas from flowing to the pilot. These issues are fairly easy to fix, but the problem could also mean that the pilot control is broken and needs to be replaced.
3. Gas Supply Issues
Your furnace obviously won’t ignite if there is no gas flowing into the unit. If you suspect this issue, the first thing to check is that the gas shut-off valve is fully open. If you have any other gas appliances like a water heater, fireplace, or range, you should also check these to see if your gas supply is shut off or interrupted for some reason.
4. Electrical Issues
Many people mistakenly believe that gas furnaces don’t need electricity to run. Electricity is obviously required to power the blower fan and enable the thermostat to signal the heating system to start, but the furnace itself also needs electricity to power its electronic igniter. This means that one of the first things you should do is check to make sure that the circuit breaker that controls your heating system isn’t tripped. Another possibility is that there is a loose electrical connection or damaged wiring that is preventing electricity from flowing to the furnace.
5. Dirty or Malfunctioning Flame Sensor
As you might imagine, the flame sensor in a furnace works to detect whether the gas flowing into the unit is lit. The flame sensor is another important safety feature that works to prevent a dangerous buildup of gas inside the furnace. It does this by controlling the furnace’s internal gas valve. When the furnace needs to light, the valve opens to allow gas to start flowing into the furnace. If the flame sensor doesn’t detect that the gas is lit within a few seconds, it will instantly close the valve to ensure gas can’t build up inside the unit and create a major safety hazard.
Flame sensors can sometimes malfunction or wear out as a result of their age, and this can cause the furnace to only ever stay lit for a few seconds before shutting down. The more common issue is that the flame sensor is coated in dirt and grime, which can prevent it from being able to detect when the furnace is lit. A dirty flame sensor can easily be fixed by having a furnace technician fully clean it. This problem can also easily be prevented by having your furnace professionally maintained every year as one part of this is cleaning the flame sensor and the rest of the furnace’s components.
6. Dirty Furnace Burners
This issue will more commonly cause your furnace to produce little heat, but it can also sometimes prevent the furnace from lighting. If the burners are completely clogged, it will prevent gas from flowing into the furnace. Dirty burners can also result in there not being the correct mixture of air and gas inside the unit. If there isn’t the right air-gas mix, the gas won’t fully combust, and this could potentially prevent the flame sensor from detecting that the furnace is lit. This is another issue that can easily be prevented and overcome by having your furnace maintained by a certified HVAC technician.
7. Thermostat Issues
There are many times when the reason that a furnace won’t ignite isn’t related to the unit itself and is instead caused by some issue with the thermostat. One possibility is that there is an issue with the wiring between the thermostat and the furnace. It may also simply be that the batteries in the thermostat are dying and no longer have a sufficient charge to signal the furnace to start. Thermostats can also fail or malfunction because of their age or some other issue, in which case the only option is to have it replaced.
There is also a chance that your thermostat isn’t properly calibrated or not accurately measuring the temperature inside the building. This is something you can easily check for by turning the thermostat up 5 or 10 degrees to see if this causes your heating system to turn on. If so, then you will need to have your thermostat tested and either recalibrated or replaced.
Expert Furnace and HVAC Services
If you’re having any issues with your furnace, you can count on the team at Reliable Ducts Heating and Cooling to help. We specialize in furnace repairs and maintenance, and our technicians can quickly determine why your furnace isn’t lighting and how to fix the problem. If the issue can’t be repaired, we can also assist with furnace replacement. We also offer a full range of cooling services as well as duct cleaning and indoor air quality solutions. If you need any heating or cooling service in the Jacksonville area, give us a call today.
