Modern furnaces work by circulating air through a system of ducts. Cold air is heated inside the furnace and is sent out to blow through registers in a ceiling or floor. Some problems can arise that will lead to a furnace not operating efficiently or not operating at all. Knowing how to troubleshoot these problems potentially could save you money by eliminating the need to call a professional for repair.
Blown Fuse or Tripped Circuit Breaker
When a furnace refuses to kick on after it has been turned on or the temperature setting on the thermostat has been increased, the first step is to confirm power to the system. A home's main service panel could have a blown fuse or tripped circuit breaker. Replace the fuse or flip the circuit breaker switch to determine whether either is the cause of the furnace not working.
Another quick check to make when you notice that the furnace has not kicked on and rooms are getting chilly is to head to the thermostat. Check the setting to make sure that another member of the household has not adjusted it to a setting where the furnace won't activate.
Closed Duct Registers
Look at the duct registers if the problem is uneven heating throughout the home. If some rooms seem much warmer than others, the problem could be as simple as duct register that is closed or partially open. Open all the registers to correct the issue.
Replace Air Filters
One good step is learning where the furnace's air filter or filters are and checking them regularly for dirt buildup that will clog circulation and limit heating efficiency. Turn off the furnace and replace the dirty filter or filters or clean the filter if it is a replaceable type.
Dirty Thermostat Contacts
The thermostat itself might be the faulty element in delivering heat. Older thermostats knocked off metal contact points could lead to less efficient heating. Reset the thermostat on the contact points. Dirty thermostats also can cause problems. Turn off the furnace and open up the thermostat's cover. Find the metal contact points and clean them with a coarse piece of paper or run a business card-sized piece of paper between the contact points.
Consult your furnace manufacturer's manual to learn how to access the system's blower. One rule of thumb is to vacuum the system's blower at the start of heating season each year. This step alone could eliminate all of the issues listed above. If you notice heavy dust and dirt on the blower blades, clean them with a soft brush. Add three to five drops of SAE 20 lubricating oil to the motor and the bearings for greater efficiency.
Misaligned Blower Belt and Pulleys
When the problem is a furnace that emits noise inside the compartment where the blower is located, it usually means that the blower belt is out of alignment. The belt should be set perpendicular to the motor shaft and the shaft and blower pulleys should be lined up together. Loosening a setscrew will allow you to realign the pulleys and belt.