Top 10 Furnace Repair Tutorials

The furnace is the most important appliance in your home. (At least it is in the winter). You depend on it to keep your family and home safe from the cold and freezing temperatures of winter. But are you really aware of the major developments in the technology used by furnace manufacturers over the years? For example, where a 50%-60% furnace efficiency was common 50 years ago, today's modern furnaces can deliver over 97% efficiency (measured in AFUE).

The type of fuel ignition system used is an important consideration in furnace design and efficiency rating. The combustion gas may be ignited by a pilot light flame (conventional furnace) or one of several types of electronic ignitions (conventional or high-efficiency furnace).

The technology used in the furnace's ignition system, heat exchanger, combustion air intake and controls will determine its efficiency and if it is considered a conventional furnace or a high efficiency condensing furnace.

The following list will provide you the best tutorials covering these furnace repair topics:

  1. Furnace Efficiency
  2. Conventional Furnace
  3. High-Efficiency
  4. Ignition Systems
  • 01 of 10

    Efficiency of Different Gas Furnace Types

    Gas water heater and furnace in basement
    Gas water heater and furnace. Jupiterimages/Stockbyte/Getty Images

    This tutorial gives you a great summary overview of conventional and high-efficiency furnace types, types of furnace burner and blower operation and of course furnace efficiency and how it is affected by different furnace feature combinations.

    The tutorial will cover the following:

    Furnace Type

    1. Conventional Furnace
    2. Condensing Furnace

    Burner and Blower Technology

    1. Single Stage Furnace
    2. Two Stage or Dual Stage Furnace
    3. Modulating Furnace
    1. Low-Efficiency Furnace: 55% to 72% AFUE (obsolete technology)
    2. Low-Efficiency Furnace: 78% AFUE (minimum AFUE allowed for new furnaces)
    3. Standard / Mid Efficiency Gas Furnace: 80% to 89% AFUE
    4. High-Efficiency furnace to 98% AFUE (Energy Star approved)
  • 02 of 10

    Troubleshooting a Conventional Gas Furnace

    Gas Furnace Schematic
    Gas Furnace. © Natural Resources Canada 2006

    Conventional furnaces have an AFUE of up to 89% and use less efficient heat exchanger technology than a high efficiency model.

    This tutorial covers possible causes and repairs for these and other conventional furnace problems:

    • No Heat
    • Not enough heat
    • Furnace cycles on and off too quickly
    • Blower does not turn off
    • Noisy operation
    • Pilot light is out
  • 03 of 10

    Repairing a High Efficiency Condensing Furnace

    hi efficiency furnace
    High Efficiency Condensing Furnace. © 2011

    The high efficiency condensing furnace has a few more troubleshooting considerations than its conventional furnace cousin. This is primarily due to different heat exchanger technology used to extract heat from the combustion process, how combustion air is delivered to the furnace and the method used to exhaust the combustion gasses.

    This tutorial will cover the following problems and issues of a high-efficiency furnace:

    Combustion Related Problems:

    • Intake air vent obstruction
    • Exhaust gas recirculation
    • Clogged condensate drain (debris, improper draining, frozen condensate)
    • Clogged flue vent
    • Testing a pressure switch
  • 04 of 10

    Anatomy of a High Efficiency Condensing Furnace

    pressure switch from a condensing furnace
    Pressure switch from a condensing furnace.

    This tutorial ​explains what makes the conventional furnace and condensing furnace so different and how and how the condensing furnace works.

    You’ll learn the following about a high efficiency condensing furnace and its components:

    • How a condensing furnace is different than a standard or conventional furnace
    • Importance of air recycling / fresh air intake
    • Fuel combustion
    • Heat extraction
    • Combustion exhaust
    Continue to 5 of 10 below.
  • 05 of 10

    Types of Plastic Vent Pipes for High Efficiency Furnaces

    CPVC pipe and fittings
    PVC / CPVC pipe and fittings.

    One of the most visible attributes of a condensing furnace is the use of plastic vent pipes for low-temperature flue exhaust and for combustion air intake. This tutorial will discuss the special plastic pipe material (most often PVC, ABS or CPVC) used for venting these furnaces including air intake, exhaust flue gas and the issue of corrosive condensation resulting from the combustion process.

    I'll also discuss the important role your HVAC contractor plays when installing these furnaces because of a lack of approved construction standards for this piping material.

  • 06 of 10

    How to Light a Gas Furnace Standing Pilot

    standing pilot
    Standing pilot in a gas furnace.

    This essential tutorial describes how to troubleshoot and light a standing pilot light in an older lower efficiency furnace usually rated at less than 80% AFUE. The standing pilot (flame is lit all the time) is sometimes referred to as a pilot light and its purpose is to serve as a small ignition flame for the gas burner. When this little flame fails to operate properly or go out, it's one of the most common reasons a gas furnace will fail to operate.

  • 07 of 10

    How to Inspect and Adjust a Gas Furnace Standing Pilot Light

    pilot light and thermocouple
    Pilot light and thermocouple.

    Even if the pilot light is lit the flame may not be properly adjusted. This tutorial will explain how to inspect and properly adjust the pilot flame for best operation.

    Once correctly adjusted, the color of the pilot light flame will look a little different depending on whether your furnace uses natural gas or propane as a fuel.

    A natural gas flame should be a bright blue with the tip of the flame having just a tinge of yellow. A propane flame should have a bluish green flame with a tinge of yellow at the tip.

  • 08 of 10

    Types of Electronic Furnace Ignition

    hot surface gas igniter
    Hot surface gas igniter.

    This tutorial provides an overview of the two main types of electronic ignition systems used in mid to high-efficiency furnaces of 80% to 90% and higher which do not use standing pilots.

    Electronic ignitions systems are typically designed one of two ways, as either a furnace intermittent pilot (IP) or as a hot surface igniter (HSI). Both systems are described in this tutorial.

    Continue to 9 of 10 below.
  • 09 of 10

    Troubleshooting an Electronic Ignition Furnace

    electronic ignition furnace
    Electronic ignition gas furnace.

    This tutorial describes how to troubleshoot and repair electronic ignition systems on furnaces using an intermittent pilot (IP) ignition system or as a hot surface igniter (HSI) system. This includes descriptions of an integrated control system and a non-integrated circuit control module.

  • 10 of 10

    How to Replace a Furnace Thermocouple or Electronic Flame Sensor

    Furnace pilot light and thermocouple
    Furnace pilot light and thermocouple.

    This tutorial shows you how to replace the device that controls the flow of fuel from the gas valve to the furnace's burner. This control device is different depending on whether the furnace uses a standing pilot or electronic ignition.

    If the furnace uses a standing pilot, then you will be replacing a device called a thermocouple. If you have an electronic ignition furnace (intermittent pilot or hot surface ignition) the device will be called a flame sensor.