Gas furnaces are fairly complicated and have a variety of components that all need to work properly for the unit to heat effectively and be energy efficient at the same time. Most every furnace will eventually need some type of repairs for it to continue functioning as it should.

Knowing when your furnace does need repairs is important since most issues will cause additional strain on the unit and lead to greater wear and tear. Not having the necessary repairs taken care of promptly can also shorten your furnace’s lifespan.

We’ve put together a helpful list of signs that you definitely need to call in the experts to have your furnace repaired!

Furnace Won’t Turn On or Turns Off Immediately

If your furnace won’t turn on at all, it usually means that either the unit has electrical issues or your thermostat isn’t working. In this situation, the first thing you’ll want to do is make sure the circuit breaker that controls your HVAC system isn’t tripped since your furnace won’t ever run without electricity. If the breaker isn’t tripped, you’ll need to have a technician check for electrical or thermostat issues and make sure the control board is functioning properly.

If your furnace turns on and the burners ignite but the unit then shuts down after only a few seconds, the issue almost certainly lies with the unit’s flame sensor. The flame sensor is a small metal probe that acts as a safety mechanism to ensure the furnace lights and stays lit. It works by sensing the heat from the burner flames. If the sensor is dirty, corroded or broken and can’t sense the heat, the control board will automatically shut off the gas supply, and the furnace will shut down. As such, the burners will only ever stay on for a couple of seconds before the gas shuts off and the flames go out. If you find this issue happens frequently, it means you’ll need to have the sensor cleaned and then tested and possibly replaced.

Furnace Runs Continuously for Long Periods

If your furnace is working properly, it should typically cycle on and off two or three times an hour and only ever run for around 10 to 15 minutes each cycle. The only times when the cycles should really ever be longer is when the outdoor temperature is below zero or your home is 7-10 degrees colder than your thermostat setting. If your furnace constantly runs for long periods, it indicates that it isn’t producing as much heat as it should for one reason or another. This most commonly happens because the air filter is dirty so this is always the first thing to check.

If replacing the filter doesn’t fix the issue, you may need to have the burners or the blower cleaned. The blower motor may also be starting to wear out, which can lead to it not being able to draw enough air into the furnace for it to heat effectively. A cracked heat exchanger can also lead to a furnace heating more slowly, and this is an extremely serious issue since it can result in carbon monoxide leaking out into the ductwork and getting blown into the rest of your home. Unfortunately, a cracked heat exchanger will usually mean you need to have your furnace replaced. It is possible to replace a heat exchanger, but the process is extremely expensive and typically only ever done if the heat exchanger is still under warranty.

Furnace Cycles On and Off Multiple Times an Hour

Short-cycling is when a furnace repeatedly turns on and off multiple times in quick succession. To put it another way, it is when a furnace shuts off before it has had time to raise the temperature in your home to whatever your thermostat is set to. Any time you find your furnace short-cycling, you should first replace the furnace filter and check to make sure that all the vents in every room are open and not clogged or obstructed by anything.

A dirty filter or closed/obstructed vents can prevent the furnace from getting proper airflow. If there isn’t proper airflow, all of the heat the furnace produces can quickly build up and cause either the furnace itself or the blower to overheat, leading to your heating system automatically turning off.

If the furnace continues to short-cycle after replacing the filter and checking the vents, you’ll need to have it inspected to determine the specific cause. It could be something as simple as the blower being clogged with dirt and needing to be cleaned or possibly an issue with your thermostat signaling the furnace to turn off too quickly. A dirty or corroded flame sensor can also cause the furnace to shut off prematurely, in which case, the sensor will either need to be cleaned or replaced.

Burners Produce Orange or Yellow Flames

When your furnace is working correctly, the flames produced by the unit’s burners should always be bright blue and steady with no flickering. If you see that the flames are flickering and are orange or yellow instead of blue, it means they aren’t fully combusting the gas. Much less heat is produced when the gas doesn’t fully combust, which means lots of energy is wasted, and the furnace will take far longer to fully heat your home. On extremely cold days, the unit may end up running almost continuously without ever really warming your home sufficiently.

Incomplete combustion is usually the result of the ports that supply gas to the burners being clogged with dust, grime and soot. In this case, all you need to do is have a technician fully clean the burners, and your furnace should work properly again. That said, you really should never have to worry about the burners being too dirty if you have your furnace professionally maintained at the start of each winter since an experienced technician will always fully clean them.

Incomplete combustion can also occur because the burners are cracked or damaged. In this case, you’ll need to have a technician replace the burners in order for your furnace to function effectively again. This is typically a fairly easy fix, but it may still be better to just replace the entire furnace if the unit is more than 10-12 years old and also has other issues.

Unusual or Loud Noises When Furnace Is Running

You’ll typically always be able to hear when your furnace is running, but the unit shouldn’t ever run extremely loudly or produce any strange noises. Rattling sounds are usually a sign of a loose component or possibly a loose air duct. If you hear a grinding sound, it often indicates that the blower is misaligned and is rubbing against its housing as it spins. A loud screeching or squealing noise is typically a sign that the bearings on the blower motor are beginning to wear out. If your heating system is older, the blower motor is possibly belt-driven. In this case, the squealing sound usually means that the belt is worn out or misaligned.

There are also situations where you may hear a loud booming noise similar to a small explosion whenever the furnace lights and this almost always means the burners are dirty or damaged. This booming sound occurs when the burners don’t light immediately when the gas starts flowing into them. This results in gas beginning to fill the combustion chamber, which creates a miniature explosion once the burners finally ignite. This type of ignition delay can be a serious issue since it can produce large flames that can easily damage the unit’s electrical components. The force of the explosion also has the potential to crack or damage the heat exchanger.

A cracked heat exchanger can also cause your furnace to produce loud popping, rattling, cracking or whistling noises. This is the main reason why you should always have your furnace inspected immediately if it does start making any strange noises since a cracked heat exchanger can put you at major risk for carbon monoxide poisoning.

Trusted Furnace Service

Any time your furnace isn’t working effectively or has any issues, you can count on Magic Electric, Plumbing, Heating + Air to repair it. Our technicians repair and service all furnace makes and models, and we can also assist with your maintenance and installation needs. If you need any type of furnace repairs in the Twin Falls area, contact us today!

company icon