| Gas Leak | If you suspect a furnace gas leak, deal with this immediately! First, if you smell natural gas in your home or near the furnace, do not light any matches or turn off or on any switches. If the gas odor is strong, immediately evacuate your house, leaving the door open. |
| Furnace Not Working—No Gas Flame | Older gas and combustion-fuel furnaces have pilot lights, whereas some newer ones have electronic ignition |
| Furnace with a Pilot Light | If your older furnace utilizes a pilot light that won’t stay lit, the thermocouple may be loose or faulty, the pilot orifice may be clogged, the pilot’s flame may be set too low, or the safety cutoff valve may be defective. |
| The thermocouple is a copper rod that the pilot flame heats-up. When it gets hot enough, the thermocouple signals that there is enough heat to burn the gas fuel being released into the appliance—and so it allows the gas to be released to the burners. In some cases where the pilot light won’t stay lit, the thermocouple needs to be adjusted or replaced. This is generally a job for a professional |
| Electronic Ignition Furnace | On an electronic-ignition furnace, turn down the thermostat or turn the power switch off and then on again to reset the ignition control module. Listen for the sound of the spark or watch for the hot surface ignitor to glow |
| Next check and clean the furnace’s flame sensor. The video below shows you how—note that this guy fixes it in about 5 minutes. We would probably use a little bit of emory paper, but he cleans the sensor with a 5-dollar bill. |
| Heating or Cycling Problems | If your furnace runs and provides some heat but not enough |
| 1-Be sure nothing is blocking the flow of warm air. |
| 2-Be sure the thermostat is set properly to “Heat” and the fan is set to “On” or “Auto.” Then try raising the set temperature 5 degrees and waiting a few minutes. |
| 3-Be sure the room heating registers are open. |
| 4-Check the filter. Because a dirty filter can reduce efficiency, replace it with a new air filter if it’s dirty |
| If your furnace cycles on and off too often | The problem is often with the thermostat—especially if you have a combustion furnace. For information on how to solve and repair this problem |
| If your thermostat has a small lever that moves along a calibrated scale that indicates “longer” (not the heat temperature lever), you can try adjusting this—the heat anticipator. Just set it one calibration mark closer to the “longer” setting if the furnace goes off and on too frequently or one mark away if the furnace allows room temperature to rise too high or drop too low before going on or off. It may take several hours for the thermostat to stabilize at this setting, so wait a while and then adjust it again if necessary. |
| Furnace Does Not Blow Air | If your furnace’s motor runs but the blower doesn’t move air, the belt that connects the two probably has broken. Replacing it is an easy fix. First, turn off all power to the unit and turn off the gas at the gas valve that serves the furnace. Remove the door on the front of the furnace cabinet to give you access to the blower (it might be on a slide-out drawer.) Check the number stamped on the belt and get an exact replacement from a home center or heating supply outlet. |
| You can usually slip the belt on the motor’s (smaller) pulley first and then start it on the blower pulley. Rotate the blower pulley by hand, holding the belt in place but keeping your fingers from getting caught between the belt and the pulley. The belt should slip right into place. If it seems to be too tight or difficult to set in place, it may be necessary to adjust the motor mount to provide more slack. |
| Then you can re-tighten the tension once the belt is in place. Check the manufacturer’s specifications for proper tension—in most cases, the belt should deflect about an inch when you press down on it. |
| Finally, some fan motors and fans need oiling; some have sealed bearings. If recommended by your maintenance manual, oil the bearings according to the manufacturer’s directions. |
| Blower Runs Continuously | Two things can cause a blower to run continuously: the room thermostat or the limit switch located on the furnace just below the plenum (the box that distributes heated air to all the ducts). The limit switch shuts off the furnace if the air in the plenum gets too hot. |
| Check the thermostat to see if the Fan switch has been turned on. If it has, turn it to Off or to Auto. If it is set to Off or Auto, the furnace’s limit switch must be adjusted. |
| Call a furnace repair technician to adjust the limit switch, or follow the instructions in your owner’s manual to reset the pointers on the fan side of the limit control. Typically, the lower pointer should be set to about 90 degrees F., and the upper one should be at about 115 degrees F. |
| Noisy Furnace or Duct Work | Many heating ducts are metal, so they conduct noise quite readily from the air-handling unit to your rooms. To break the conduction of sound, you can have a heating contractor insert flexible insulation duct work between the furnace or air conditioner and the duct work runs. |
| Pinging or Popping Sounds | A pinging or popping sound coming from the duct work can come from thermal expansion—the ductwork expanding and contracting as it heats and cools. Or, air blowing past a loose flap of metal can make the sound. Track along the duct runs, listening for the sound. If you locate it, make a small dent in the sheet metal to provide a more rigid surface that’s less likely to move as it heats and cools. |
| Rattling Noises | If the furnace cabinet makes rattling noises when it runs, be sure the cover panels are screwed on tight. Tighten any loose panels. |
| Squealing Noises | Squealing sounds from a forced-air furnace generally occur when the belt that connects the motor to the fan slips. Tighten the fit by adjusting the motor mount. Or, the belt is improperly aligned or worn and needs replacement. Follow the instructions in your owner’s manual. |
| This job involves removing the access panel, loosening a couple of bolts that hold the blower motor at the proper tension, and adjusting its distance or realigning the belt. In many cases, it’s a good idea to remove the belt and buy a replacement at a home center. Last, when reinstalling the belt, be careful not to over-tighten it; this can wear out the motor bearings. |
| Grinding Sounds | If the blower is making a grinding noise, shut off the unit and call a furnace repair technician; the motor’s bearings are probably shot. |
| Furnace Not Working—Oil Burner | First of all, if the oil burner goes on and off too much, clean or replace the filter. |
| If your oil burner doesn’t work at all, check to see if it is receiving electrical power, if the thermostat is broken or turned off, or if a flame sensor in the burner or heat sensor in the stack has signaled the unit to shut off. |
| In the event that replacing the filter or checking these issues don’t solve the problem, call a furnace repair technician because oil-burning furnaces are complex to repair. |