Top Furnace Troubleshooting and Repair Tutorials

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)

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

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

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

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.

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.

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.

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.

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.

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.