Woodstock Heating & Air

Published On July 3, 2018 | By admin | Home Improvement

Furnace Repair Troubleshooting Guide

Repairing your own furnace can be time consuming and frustrating.  Yet, calling a HVAC Contractor for a furnace repair can be expensive and unnecessary.  As much as I love to troubleshoot and repair furnaces, it’s very satisfying to teach homeowners how they can do simple furnace repairs on their own.  With a little knowledge about your furnace, you can troubleshoot some simple repair issues at little or no cost.

It is important to understand that if you do not immediately repair a furnace, you run the risk of further damaging your furnace.  When you deal with repairs at once, you extend the life of the furnace, you keep your energy costs at a Woodstock Heating & Air minimum and more importantly, you allow your family to be comfortable and safe.

Here are five simple steps that can help you save a few dollars by repairing your furnace yourself.

Thermostat Malfunction


The furnace does not produce heat; wild temperature swings; uneven heating; frequent on and off cycles.

Possible Cause

The thermostat controls the temperature and heat flow in your home. When the temperature in a room does not match the thermostat’s temperature, the heat source will turn on. When it matches, the heat source turns off. In short, the thermostat controls the “on and off” cycles of your heat source.

When your furnace is not producing enough heat, first check the thermostat. A malfunctioning thermostat is often the underlying problem for a furnace that does not produce heat or a fan that does not run.

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Some thermostats are connected to your home’s electrical system. Some thermostats are battery operated.


Before calling an HVAC technician, check the thermostat:

  • Temperature Setting. The thermostat must be in the “heat position” and you must adjust the temperature setting to a level that makes the room comfortably warm.
  • Change Batteries. Most thermostats powered by batteries have a “battery low” signal. If no signal, change the batteries regularly.
  • Wirings or Loose Connections. For electric thermostats, check if there is a power supply. Also check on the connection between the thermostat and the furnace. A loose or worn connection between the thermostat and the furnace will result in the furnace not turning on and off frequently.

After doing these and your furnace still does not produce heat or the fan still does not kick in, it may be time to replace your thermostat.

Air Flow Problem


Furnace overheating; limited or no heat

Possible Cause

If your furnace is overheating and not working properly, it may not be getting enough air. An overheating furnace (caused by low or no air flow from indoor vent registers) can shut down completely or in extreme cases, start a fire. There may also be something wrong with the fan motor, belts or bearings. Limited air flow can cause damage to the furnace motor and other components.


  • Worn Out Components. Check if the fan belt has worn out. If it is, replace it.
  • Greasing. Bearings of some old furnaces need to be greased regularly.
  • Vent Blockages. Leaves or snow can block outside vents. Turn off the power of your furnace before clearing any blockages from outside vents.

If your furnace still has limited or no heat after performing these steps, call an HVAC technician.

Clogged Filters


Poor air quality; limited or no heat; overheating heat exchanger; low air flow; heating comfort

Possible Cause

Simply, dirty and clogged filters cause poor indoor air quality by restricting air flow. When you feel no heat even with the blower running, it is time to replace your filters. A dirty filter will also cause soot to build up on the heat exchanger. This will reduce the efficiency and life expectancy of the furnace.


Before removing filters, shut off the furnace and the thermostat. Refer to the owner’s manual for your furnace to check the right way to remove and re-install filters. It will also include recommendations on how many times you can clean your filters before eventually replacing them.

If you are not confident you can handle your furnace filters, call a professional heating and cooling contractor.  

Pilot or Ignition Control Problems


The pilot light is out; pilot light does not stay lit

Possible Causes

The pilot light or ignition control of your furnace ignites the gas each time a heating cycle starts. Problems with the light or ignition controls occurs when the pilot light housing is dirty, causing the thermocouple (a device that makes sure the pilot light is on before the gas turns on)  to malfunction.  It can be dangerous for the gas to turn on if it cannot be ignited. It can cause a fire.


If you notice no warm air coming out of the vents, see if the pilot light is lit. If the pilot light does not light, try doing any of these:

  • Fully depress the pilot light.
  • Check that the gas valve is fully open.
  • Slightly tighten the thermocouple nut.
  • Adjust the pilot to make the flame about two inches long.

If none of these steps work, call an HVAC expert.  



Humming noise; squeaky noise; rattling sound

Possible Causes

An overly noisy furnace could be caused by any of these:

  • Damaged working parts caused by dirt build-up on the filters
  • Dirty gas burners.
  • Unlubricated ball bearings.
  • Failing motors (Humming noise).
  • Gas leaks: carbon monoxide leak because of a possible crack in the heat exchanger (Rattling sound).
  • Overworked furnace without proper maintenance.


  • Clean or replace filters.
  • Have your furnace thoroughly cleaned.

If you have changed your filters and still the odd sounds from the furnace persist, call an HVAC technician. A noisy furnace can be an urgent issue which needs to be remedied immediately.

If you are confident you can handle your furnace with ease, try to troubleshoot your furnace before calling in an HVAC technician. Continued use of a furnace that is not working properly is prone to major repairs and shortened life span.

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