A leak is the most obvious sign. If you spot one, it’s time to call a technician to track down the source and get it fixed.

Strange noises coming from your furnace are another red flag that something needs attention.

If you turn up the thermostat and don’t feel any heat coming from the vents, that could point to an efficiency issue. Sometimes it’s a quick fix, but if the problem runs deep, it may mean the unit needs to be replaced.

If people in your home aren’t feeling well, that’s worth paying attention to as well. Poor air quality from a struggling furnace can trigger asthma symptoms and worsen allergies.