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Top Furnace Troubleshooting and Repair Tutorials


Top 10 "Must Read" Furnace Repair Tutorials:
The furnace is the most important appliance in your home. 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, todays modern furnaces can deliver over 97% efficiency (measured in AFUE).

The type of fuel ignition system used is 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:
  • Furnace Efficiency
  • Conventional Furnace
  • High Efficiency Furnace
  • Ignition

1. Gas Furnace Types and Their Efficiencies

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 efficiencies and how they are affected by different furnace feature combinations.

The tutorial will cover the following:

    Furnace Types
  • Conventional Furnace
  • Condensing Furnace
    Burner and Blower Technology
  • Single Stage Furnace
  • Two Stage or Dual Stage Furnace
  • Modulating Furnace
    Furnace Efficiency Ratings
  • Low Efficiency Furnace: 55% to 72% AFUE (obsolete technology)
  • Low Efficiency Furnace: 78% AFUE (minimum AFUE allowed for new furnaces)
  • Standard / Mid Efficiency Gas Furnace: 80% to 89% AFUE
  • High Efficiency Gas Furnace: 90% to 98% AFUE (Energy Star approved)

2. Troubleshooting a Conventional Gas Furnace

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

3. Troubleshooting a High Efficiency Condensing Furnace

© Home-Cost.com 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 gases.
    This tutorial will cover the following problems and issues of a high efficiency furnace:
    Combustion Related Problems:
  • Intake air vent obstruction
  • Exhaust gas recirculation
    Ignition Related Problems:
  • Clogged condensate drain (debris, improper draining, frozen condensate)
  • Clogged flue vent
  • Testing a pressure switch

4. Anatomy of a High Efficiency Condensing Furnace

in this tutorial called Anatomy of a High Efficiency Condensing Furnace I explain 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
  • Air recycling / fresh air intake
  • Fuel combustion
  • Heat extraction
  • Combustion exhaust

5. Types of Plastic Vent Pipes for High Efficiency Furnaces

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.

6. How to Light a Gas Furnace Standing Pilot

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.

7. How to Inspect and Adjust a Gas Furnace Standing Pilot Light

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.

8. Types of Electronic Furnace Ignition

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.

9. Troubleshooting an Electronic Ignition Furnace

electronic ignition 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. How to Replace a Furnace Thermocouple or Electronic Flame Sensor

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.

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