DIY Forced-Air Heating and Furnace Repairs

The following are simple repair solutions to help you remedy some common forced-air furnace problems:
Problem 1: No heat
The good news is when your heating system isn’t heating, the problem is generally due to thermostat malfunctions, a blown fuse, tripped circuit breaker, or if you have a combustion furnace, the pilot light has more than likely gone out.  The following are some quick checks for when your heat doesn’t come on even after you have adjusted the thermostat to a setting above the current room temperature:
1.      Make sure that you have the thermostat is set to “Heat.”  This is for those of you who have a combined heating and cooling system.  We receive approximately 30 calls a year because of this simple problem.  This usually occurs when one person in the home has turned off the heat for one reason or another.  If the thermostat isn’t turn to Heat, please do so.  If you still are not getting heat, then go to step 2.
2.      Check the furnace’s circuit breaker to ensure that it is in the on position or that the fuse has not blown.  Make sure that you check both the main electrical panel and any secondary sub-panels that you may have that supplies power to the unit.  If the circuit is blown or is tripped, then reset the breaker or replace the fuse.  However, if the circuit trips again or the fuse blows again, then call an electrical contractor as the problem is probably is a short in the electrical system that provides power to the furnace.  Do not attempt to repair the short yourself unless you are an experienced electrician.  If the circuit is not tripped or the fuse blown, then make sure that the furnace’s power switch is turned on.  If the power switch is not on, turn it on.  It will take a couple of minutes for your furnace to engage.  If this does not work then proceed to step 3.
3.      If after all of this, the problem might be that the blower motor may need to be reset.  This could be because of an overload.  Look for a RESET button that is usually located near the blower motor’s housing.  Once you have located the reset button, press it.  If there is no response, allow the motor to cool down for approximately 30 to 45 minutes, and then try the RESET button again.  
4.      If at this time you still do not have heat, turn off the power to the furnace at the main electrical panel or sub-panel.  Check to see if there is a fuse in the power switch.  If there is one there, see if it is blown.  If it has, replace the fuse, making sure that you follow the instructions in your owner’s manual.  If you have misplaced the owners’ manual or are not sure about what it will take to replace the fuse, than we strongly suggest that you call a furnace repair technician.
5.      If you have a gas furnace, and are getting heat, then check to see if the pilot light has gone out or if the gas valve has been shut off.  Check the furnace’s ignition, as follows:
A.     In order for your gas- or oil-burning furnace to heat, it must be receiving fuel.  If you have a gas-fired furnace, make sure the valve on the gas pipe is turned on.  The handle should be in line with the gas pipe.  If you have an oil furnace, check your fuel supply.
B.     Check the furnace to see if the pilot light is lit.  If it is not lit, then follow the instructions in your owner’s manual or the instructions posted inside the furnace cabinet for pilot light information. 
6.      If it still doesn’t work, be sure the thermostat isn’t faulty.  Click here for troubleshooting a Thermostat. 
7.      If after trying each of these steps, your furnace still does not work, call a heating contractor or furnace repair technician.
Problem 2: Insufficient heat
If your furnace is operating, but providing little heat make sure that there isn’t anything blocking the warm airflow.
1.      Check to see if your thermostat is set properly.  If it is, then raise the set temperature 5 degrees and waiting a few minutes to see if that improves the amount of heat in the room.
2.      Make sure that all of the room’s heating registers are open.
3.      Check the furnace filter and if it is dirty, clean it if you have reusable filter, or replace it if you use a disposable filter.
4.       If after following these simple steps, your furnace still does not work, call a furnace repair technician to check out your system.
Problem 3: Furnace constantly turns on and off
If your furnace continues to run or cycles off and on too frequently, then the problem will often be with the thermostat.  This is especially true if you have a combustion furnace.  Click here for troubleshooting a Thermostat.
If you have an electric-resistance furnace, or heat pump that frequently turns off and on, the problem is often due to the unit overheating because of a clogged filter or blower, which is malfunctioning.  Cleaning or replacing the filter.  If this does not correct the problem, then contact a furnace repair technician.
Problem 4: Dramatic changes in room temperature
If the room temperature drops more than about 3 degrees, between the time your furnace shuts off, and the time it turns back on, or it the room temperature raises more than 3 degrees from what the set temperature is set on the thermostat, it generally means that the furnace isn’t cycling on and off often enough.  This problem is usually caused by the thermostat being improperly calibrated or installed where it doesn’t sense a proper sampling of room air.  Contact a furnace repair technician.
Problem 5: Blower runs continuously
If your blower continuously runs, the problem may be caused by two things, first the problem may be due to the thermostat mounted on the wall, or second the limit switch located on the furnace.  The limit switch is usually located on the furnace right below the plenum, which is the box that distributes the heated air to the ducts.  The job of the limit switch is to shut off the furnace if the air inside the plenum gets too hot.
Another reason for the blower to run continuously is if the “Fan” switch on the thermostat has been turned on.  If the fan switch is turned on, then turn it to the “Off” or “Auto” position.  However, if the switch is set to the off or auto position, then your furnace’s limit switch must be adjusted.  If you have are handy with this type of repair, follow the instructions in your owner’s manual to reset the pointers on the fan side of the limit control.  However, if you are not handy or comfortable with this type of repair, then we strongly suggest that you call a furnace repair technician to adjust the limit switch.  
Problem 6: Noise Furnace
If you hear squealing sounds coming from your forced-air furnace, this is often due to the belt that connects the motor to the fan slipping.  In many instances, the belt has been improperly aligned or is worn and in need of replacing.  To replace or properly align the belt, follow the instructions in your owner’s manual.  If you do not have or have misplaced your owner’s manual, contact the manufacturer, and request one.
Replacing the belt will involve removing the access panel, loosening a few bolts, which secure the blower motor at the proper tension, and then replacing, and aligning the belt.  Even if the belt appears in good condition, it is a good idea to remove the belt and purchase a new replacement at the hardware store.  When you replace the belt, make sure that you do not over-tighten it as this can cause the motor bearings to wear out quickly.
After you have replace the belt, if your furnace starts making rattling noises, then check the cover panels to ensure that it is screwed on tight. 
However, if you hear a grinding noise coming from the blower, turn off your unit and call a furnace repair technician.  A grinding noise coming from the blower usually means the motor’s bearings are shot.
Problem 7: Noisy Air ducts
Having noisy air duct is a more common problem than most people thing.  The reason is that most heating ducts are metal, which will expand and contract as it heats up and then cools down.  Another reason for air ducts being noisy is they will conduct sounds from the air-handling unit to your rooms.  If you want quieter air ducts, consider having a heating contractor insert flexible insulation ductwork between the furnace or air conditioner and the ductwork runs, this will reduce the amount of noise coming from your air ducts.
Popping noises coming from your ductwork is often caused by thermal expansion.  However, it can also be due to air blowing past a loose flap of metal.  To discover what is causing the popping sound, follow the duct runs, carefully listening for the sound.  Once you have located where it is coming from, you want to make a small dent in the sheet metal.  By making a small dent, you will make a more rigid surface that will be less likely to move when it is heated and cooled.

 

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