Furnace Makes Noises

Problem: Furnace makes unfamiliar noises when operating.

Background: Sometimes homeowners think their forced-air furnaces need to be replaced because they make strange noises. But the cause may be a simple mechanical problem with the motor or fan within the blower system. Sometimes making simple adjustments and / or replacing a part will solve a strange noise problem.

What to do: Turn off the power to the furnace, remove access panels, and make a careful examination of the blower area. Check to make sure that the drive belt between the motor and the blower has proper tension, is in alignment, and is not cracked.
Also check the pulley on the motor, making sure that it is not loose on the shaft, has worn grooves, or is dirty. If loose, retighten any set screws. If worn or dirty, remove the belt, clean the pulley, and sand down its interior sides. Also check the pulley on the blower fan. Spin the blower to check for sound which may be caused by something inside. If the fan is rubbing against the housing, it needs to be adjusted and your best bet is to call a technician. Push and pull on blower pulley to check for end-play. If excessive, shaft collars need to be adjusted.

Special advice: A blower that needs oil may also make noises. Follow owner manual instructions to oil. Sometimes oil-less bearings wear out and need replacement. To see if the motor is making the noise, re move the belt and run the motor; the motor may simply need oiling, but motor bearings may still make noise.
If so, decide if you can live with the noise or if you want to replace the motor. A dirty furnace filter can also cause noise; clean the filter as recommended.

Helpful hint: If the burner of a gas furnace makes an unusual noise, the gas input amount may not be correct, or it may be getting too much primary air. In either case, contact a service technician. Also, contact a technician immediately if the walls or windows in your home sweat excessively. The furnace may not be getting enough ventilation or the flue pipe may be blocked.

Furnace Doesn’t Work

Problem: Furnace is dead, or doesn’t turn on when the thermostat is raised.

Background: What are often thought to be furnace emergencies are caused by the thermostat being set or operated wrong, by having the power to the furnace cut off, or by not having fuel or a working pilot light. (Important: If you detect gas odor in your home or in the furnace area, take immediate precautions.

What to do: First double-check to be sure that power is reaching the furnace. Check the circuit breakers or fuses at the main service box. If reset breakers or replaced fuses blow again, call a service technician. Also check to see that any switches on or near the furnace are turned on. Be sure that the thermostat is set in the “heat” position, and that it is set above room temperature. If the furnace doesn’t come on after an interval, check the furnace itself. If you have a gas furnace, the gas valve should be turned to “on.” If you have an oil furnace, check the fuel level in the tank. If the furnace has a pilot light, check to make sure that it is lit. If not, relight it carefully, following the instructions in the owner’s manual or on the unit.

(Warning: If you smell gas, leave the area immediately and call a technician. The lighting instructions for a gas furnace should explain the procedure to use to determine whether the gas valve is good. If the test procedure indicates the gas valve is bad, turn off furnace gas valve and main gas valve and call a technician. Also call for help if the pilot light does not stay lit after several tries.)

Special advice: Most furnace controls will have a reset switch. If the furnace starts after the reset switch is pushed, but shuts off again, call a technician. Gas furnaces equipped with an electronic ignition device, instead of a pilot light, have a gas valve designed for slow opening. It first opens part way to let just enough gas through for safe ignition of the burners. After a few seconds it opens fully to allow proper flame height. The burners should light within 2 seconds after the gas valve opens. If air in the valve and lines prevents the flame from being established within 6 seconds or so, the system will go into “lock-out.” To reset, wait 1 minute and turn the thermostat to a setting below room temperature. Then turn back up to a setting above room temperature; this should re-start the ignition cycle.

Helpful hint: If the furnace works, but heat is not circulating, the problem may be with the blower or the blower belt. If the flame on burner is yellow or blue, or lifts off of the burner, call for a technician to adjust. Check your owner’s manual for annual maintenance suggestions and keep the furnace and its components free of lint or dirt accumulation.