With most of your furnace hidden from regular view, it can be hard to detect and diagnose problems until they get serious. Knowing what signs to look for, like strange smells and noises or abnormal operating behavior, can help you figure out problems and contact a professional for quick repairs before anything gets worse.
Loud, Irregular Noises
Even when functioning correctly, your furnace will make a variety of noises, but there are some you should not ignore.
If you hear a loud banging sound whenever your furnace turns on, this could mean your burners are dirty and causing a buildup of gas to occur before the furnace finally ignites. Likewise, rattling sounds that are louder than usual could mean your ducts need repair or that there's a leak somewhere.
Sounds like shrieking or metal-on-metal noises could be something as innocuous as a belt that needs to be replaced, or it could be something wrong with your blower motor, such as a loose part or bearings that are not properly lubricated.
Humming sounds point toward an electrical issue, which can happen even if your furnace is still running, or an issue with your fan. Generally, the type of problem your furnace has can be narrowed down by what type of noise you're hearing, but a professional inspection is still a good idea if you hear anything out of the ordinary.
Strange or Foul Smells
With some exceptions like burning dust after long periods without use, the air coming from your vents won't have a strong odor to it. Since it's pulled from your home, it should just smell like the air near your intake vent. If you do start smelling something unusual, however, this can point to specific issues depending on what that smell is.
For example, if there is a consistently musty odor from your vents, you could have mold growing either in or near your ducts. Burning plastic smells might mean that some of your components' wiring is starting to burn. If you smell rotten eggs or something like dirty socks, there could be a gas leak, a clogged gas vent, or a failing heat exchanger.
Because these problems can so often be potentially harmful to you and anyone else who lives in your home, it's a good idea to avoid using your furnace again until the problem has been fixed.
Repeated Breaker Tripping or Short Cycling
When it's working properly, your furnace will run until the temperature in your home matches the temperature you set on your thermostat no matter how long or short a time it takes. If your furnace continuously shuts itself off before your inside temperature is what it's supposed to be, or never runs for more than a few minutes at a time, your furnace could be short cycling. This can be caused by a fault in one of the furnace's components or another issue that's triggering your furnace's safety shut-off feature.
If your furnace keeps shutting off because the breaker of the circuit it's installed on keeps tripping, this could indicate a problem with a part like a capacitor, or it could also mean there's a problem with the circuit itself, and that the breaker is tripping to prevent any damage. Two examples of issues that could cause this problem are short circuits and ground faults, both of which should be investigated and fixed immediately to prevent the possibility of electrical damage to your furnace or to your home itself. Contact a company near you for assistance with furnace repair.