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As a technician or novice servicer, this chapter on gas is very important to the
safety and technical knowledge that is needed to repair major gas appliances. In
addition, consumers should be knowledgeable about safety procedures and basic
characteristics of natural and liquefied petroleum gas (LP or LPG). Any person who cannot
use basic tools or follow written instructions should not attempt to install, maintain, or
repair gas appliances.
If you do not fully understand the procedures in this chapter, or if you doubt your ability
to complete the task on your gas appliance, please call your service manager.
Currently, gas is used in millions of homes for heating, cooling, cooking, drying laundry,
and water heating. Understanding gas theory, gas conversion, ignition systems, and the
different types of gases used is something that every technician needs in his arsenal to
service gas appliances. In addition, the technician needs to understand two other important
elements when servicing gas appliances: combustion and ventilation. Some appliances use
only gas as the main fuel, while others use gas and electricity. Although this chapter cannot
cover all there is to know about gas, it provides the basics.
The following are a few safety tips to help you in handling major gas appliances in your home:
•Always follow the manufacturer’s use and care manual for the gas appliance.
•Always keep combustible products away from gas appliances.
•Keep your gas appliance clean from soot, grease, and food spillages.
•Teach your children not to play near or with gas appliances.
•Always have a fire extinguisher nearby just in case of mishaps that might lead to a fire.
•Have a smoke detector and a carbon monoxide detector installed in the home, and
check the batteries yearly.
•Never use a gas range to heat the home.
•Make sure that gas appliances have proper venting according to the manufacturers’
Types of Gas
The two most common gases that are used in homes today are natural gas and liquefied
petroleum gas (LP or LPG). Gas is a form of chemical energy, and when it is converted by
combustion, it becomes heat energy. This type of heat energy is used for cooking, drying,
heating, cooling, and lighting.
Natural gas is a naturally occurring product made up of hydrocarbon and non-hydrocarbon
gases. The main ingredient found in natural gas is methane (70 to 90 percent), with the
remainder of the ingredients being nitrogen, ethane, butane, carbon dioxide, oxygen,
hydrogen sulphide, and propane. These gases are located beneath the earth and can be
removed through constructed wells. Another method for producing and harvesting natural
gas is through landfills. The methane gas that is produced by the decomposition of materials
can be harvested and added to the natural gas supply.
The heating value of natural gas is between 900 and 1200 BTUs per cubic foot. The air
we breathe has a specific gravity of 1.00, and natural gas is lighter than air, with a specific
gravity varying from 0.58 to 0.79. Natural gases are odorless and colorless—gas companies
add an odor agent to warn for leaks.
The pressure of natural gas that is supplied to a residence will vary, between a 5- and
9-inch water column. A gas pressure regulator that is connected to the appliance will further
reduce the pressure. For example, on some gas ranges the pressure will be reduced to a 4-inch
water column, while on other models the pressure might be a 6-inch water column. On some
water heaters manufactured today, the pressure is between a 4- and 7-inch water column.
To determine the correct pressure rating, the technician must refer to the manufacturer’s
specifications or the installation instructions for that product.
Liquefied Petroleum Gas
Liquefied petroleum gas (LP or LPG) is obtained from natural gas sources or as a by-product
of refining oil. LP gas for domestic use is usually propane, butane, or a mixture of the two.
This type of gas is compressed and stored in storage tanks under pressure in a liquid state at
approximately 250 pounds per square inch. The pressure in an LP tank will vary according to
the surrounding temperatures and altitude. LP gas tanks can be transported to areas that are
not supplied by natural gas supply lines.
The heating value of propane gas is 2500 BTUs per cubic foot, with a specific gravity of
1.53. The heating value of butane is much higher—about 3200 BTUs per cubic foot, with a
specific gravity of 2.0. Liquefied petroleum gas is heavier than air and will accumulate in
low-lying areas on the floor, in an enclosure, or in pockets beneath the ground, creating a
hazard if it encounters an open flame. As mentioned, these gases are odorless and colorless,
and gas companies add an odor agent to warn of leaks.
LP or LPG gas pressure for residential appliances, as established by the gas industry,
will be between a 9- and 11-inch water column. To determine the correct pressure rating, the
technician must refer to the manufacturer’s specifications or the installation instructions for
Combustion is a rapid chemical reaction (burning) of LP or natural gas and air to produce
heat energy and light. To sustain combustion in a gas appliance, an ignition source—such as
that produced by a flame or by electrical means—is used to ignite the gas vapors. Three
elements are needed to produce a flame when burning gas vapors: fuel, heat, and oxygen.
If any one element is missing, flame or burning of gas vapors will not exist (Figure 8-1).
It takes 1 cubic foot of gas mixed with 10 cubic feet of air to have complete combustion
of natural gas. The process produces approximately 11 cubic feet of combustion product,
consisting of approximately 2 cubic feet of water vapor, 1 cubic foot of carbon dioxide,
8 cubic feet of nitrogen, and the excess air from the gas appliance. These combustion
products must be properly vented or discharged safely from the gas appliance.
It takes 1 cubic foot of gas mixed with 24 cubic feet of air for complete combustion to
happen with propane gas. The process produces approximately 25 cubic feet of combustion
product. With butane gas, it takes 1 cubic foot of gas mixed with 31 cubic feet of air and
produces 32 cubic feet of combustion product (Figure 8-2). With the proper mixture of air,
gas, and flame, complete combustion will take place. The combustion product that is
produced from complete combustion will be carbon dioxide and water vapor.
Inadequate venting of a gas appliance will restrict the flow of air into the gas appliance.
This lack of proper ventilation will reduce the amount of oxygen within the air for complete
combustion to occur. The air that we breathe is a mixture of gases containing nitrogen,
oxygen, argon, carbon dioxide, water vapor, and other trace gases (Figure 8-3). Incomplete
combustion will cause the reduction of oxygen levels in the air supply within a room.
Proper ventilation—adequate fresh air into the room—is important and cannot be stressed
enough for the proper operation of a gas appliance, as well as for the safety of human life
within the home.
Carbon monoxide (CO) is a toxic gas that can cause death if inhaled in copious amounts.
It is odorless, colorless, and has no taste. The human body cannot detect carbon monoxide
with its senses. When carbon monoxide is inhaled, it is absorbed into the bloodstream and
stays there longer, preventing oxygenated blood from performing its job in the body. Two
factors affect the amount of carbon monoxide absorbed into the bloodstream: the amount of
carbon monoxide in a room and the length of exposure. Lower levels of CO inhalation can
cause flu-like symptoms, including headaches, dizziness, disorientation, fatigue, and nausea.
Other exposure effects can vary depending on the age and health of the individual.
Carbon monoxide in homes without gas appliances varies between 0.5 to 5 parts per
million (ppm). CO levels in homes with properly maintained gas appliances will vary from
5 to 15 parts per million. For those gas appliances that are not maintained properly, carbon
monoxide levels may be 30 ppm or even higher.
Testing for Carbon Monoxide
Consumer products for detecting carbon monoxide in a home have been on the market for
years. Carbon monoxide detectors should have an alarm that alerts consumers before they
are exposed to hazardous levels of carbon monoxide. In order to prevent false alarms, CO
detectors must be able to distinguish carbon monoxide gases from other types of gases, such
as butane, heptane, alcohol, methane, and ethyl acetate. Two manufacturers that you can
visit on the Internet to view the different types of carbon monoxide detectors available are
www.kidde.com and www.firstalert.com.
Technicians who test for carbon monoxide use a special handheld meter to check the
levels of carbon monoxide in a room or home. For a handheld carbon monoxide test meter,
Properties of Natural gas Propane Butane
Chemical formula C3H8 C4H10
Boiling point of liquid at atmospheric pressure°F −44 32
Speciic gravity of vapor (air = 1) 1.53 2.00
Speciic gravity of liquid (water = 1) 0.51 0.58
BTU/cubic foot 2516 3280
Caloriic value @ 60°F BTU/gallon 91,690 102,032
BTU/lb 21,591 21,221
Latent heat of vaporization BTU/gallon 785.0 808.0
Liquid weight lbs/gallon 4.24 4.81
Vapor volume from 1 gallon of liquid at 60°F Cubic foot 36.39 31.26
Vapor volume from 1 lb of liquid at 60°F Cubic foot 8.547 6.506
Combustible limits % of gas in air 2.4–9.6 1.9−8.6
Amount of air required to burn 1 cubic foot of gas Cubic foot 23.86 31.02
Ignition temperature in air°F 920−1020 900−1000
Maximum lame temperature in air°F 3595 3615
100 Over 100 92
All data are approximate.
FIGURE 8-2Properties of utility gases.
When to check for carbon monoxide in a home:
•When the consumer complains of headaches or nausea
•Houseplants are dying
•Unknown chronic odors from unknown sources
•Condensation on cool surfaces that might lead to flue gas products in the home
Figure 8-4 illustrates the locations in a home to test for carbon monoxide gas. These tests
should be conducted near gas appliances, gas heating systems, heating ducts, and the
atmosphere in a room, approximately 6 feet above the floor.
When testing for CO in a gas appliance that has not been running for a while, you should
follow these steps:
1. Test the air near the appliance and the surrounding air in the room before you turn
on the appliance.
2. Test the air after you turn on the appliance.
3. Test the air near the appliance after the appliance has been running for 15 minutes.
Composition of air.
The air we breathe is
made up of 99.99
percent of nitrogen,
dioxide, and argon.
Nitrogen Oxygen Argon Carbon dioxide
Component Volume Symbol
Ammonia Trace NH3
Argon 0.93% Ar
Carbon dioxide 0.03% CO2
Carbon monoxide Trace CO
Helium 5.2 ppm He
Hydrogen 0.5 ppm H2
Iodine 0.01 ppm I2
Krypton 1.1 ppm Kr
Methane 2.0 ppm CH4
Neon 18.2 ppm Ne
Nitrogen 78.08% N2
Nitrous oxide 0.5 ppm N2O
Oxygen 20.95% O2
Sulfur dioxide 1.0 ppm SO2
Water vapor 0 to 5% H2O
Flue gases are the by-products of combustion that are exhausted through a chimney or flue
to the outside of the home. These gases consist of the following:
•Nitrogen (colorless, odorless, and tasteless) The air we breathe is made up of
79 percent nitrogen.
•Carbon dioxide (colorless and odorless) The human respiration process produces
•Oxygen (colorless, odorless, and tasteless) Oxygen is the main ingredient for
•Carbon monoxide (colorless, odorless, and tasteless)
•Nitrogen oxide (colorless and odorless) Nitrogen oxide forms in the combustion
process of gas fuels.
•Sulfur dioxide (colorless and smells like burnt matches) Sulfur dioxide is irritating
to the lungs.
•Hydrocarbons (colorless, odorless, and tasteless) Hydrocarbons are found in
natural and liquefied petroleum gases.
•Water vapor Approximately 10 percent will be vented through the flue or chimney.
•Soot The remains of incomplete combustion.
Prior to the invention of the Bunsen burner in 1842, gas burners would produce a yellow
flame for light and heat. The process allowed the gas to enter into a tube, expel through a
port, and, when lit with an ignition source, the gas would burn without pre-mixing the air
before it left the burner (Figure 8-5). As the flame burned, the gas temperature began to rise
within the flame. Without the presence of pre-mixed air and gas, carbon particles began to
pass through the flame, causing it to turn yellow. As more air was introduced into the
combustion process, the flame would turn blue or blue with yellow tips.
Appliance manufacturers had the freedom to tailor the flame patterns from the Bunsen
burner design to design gas appliances. The Bunsen burner worked on the principle of
introducing air into the mixture of the gas before it left the burner port. An orifice was used
to regulate the gas flow within the burner body (Figure 8-6). Attached to the burner body is
an adjustable shutter to control the primary air mixture that enters into it. The flame that is
of complete combustion
Complete combustion of
Zone of partial combustion
Unburned mixture of gas
and primary air
produced by the Bunsen burner has multiple colors within it. Each color within the flame
marks a stage of the burning process of gas (Figure 8-7). The stages are as follows:
•The inner cone is the first stage of the burning process. Within this cone the gas is
burned, which forms by-products, such as aldehydes, alcohols, carbon monoxide,
•The outer cone surrounds the inner cone, and as air diffuses into the flame, it
continues the burning process. If enough air is present during the burning process,
the by-products from the inner cone will burn up in the outer cone. The by-products
that are produced in the outer cone are carbon dioxide and water vapor.
•The outer mantle that is produced by the Bunsen burner is nearly invisible, with
all the gas burned up. The reason it glows is due to the high temperature produced
by the complete combustion of the gas products from the outer cone.
FIGURE 8-7Different lame types of a Bunsen burner, depending on the amount of oxygen supplied.
Unburned air and
The temperature of a flame can vary, depending on what type of gas is used and how
much air is pre-mixed with the gas. Temperatures within the flame will vary; the inner cone
is cooler than the outer cone, and the hottest flame temperature is just above the outer cone.
When air is mixed with gas before it leaves the burner port, it is known as the primary air
supply. Under ideal conditions, most burners only use 50 percent of the primary air supply
to burn the gas, and the remaining 50 percent of the air is supplied by the secondary air
supply from around the flames. In reality, additional excess air is needed to ensure that
enough air is present to completely burn off the gas. The total air supply is accomplished by
adding the sum of the primary, secondary, and excess air supplies. The total air supply
needed for combustion is measured in percentages of air needed for complete combustion.
Every manufacturer has its own specifications in the installation instructions or service
manual for the total air percentages needed for the appliance model that you are servicing.
The appearance and stability of a flame is influenced by the amount of the primary air
supply, the gas-burning speed, and the burner port. When the primary air supply is at
100 percent, under ideal conditions, the speed of burning is at its maximum. The speed of
burning is also affected by the type of gas being burned. The flow velocity of the gas
depends on the size of the orifice—the smaller the orifice size, the greater the flow velocity.
Flow velocity from a burner port will also vary, depending on the size of the opening, with
the greatest flow from the center of the port (Figure 8-8).
After the air-gas mixture leaves the port, the flow velocity slows down, and the flame
begins to stabilize when the flow velocity equals the burning speed. At the same time, the
flame cone begins to take shape when the flow velocity of the air-gas mixture levels off
when it leaves the burner port. The burning speed increases and the flame temperature
increases near the top of the flame cone. Therefore, the shape of the flame cone is rounded
off at its tip. The inner cone is determined by the effects of the velocity away from the
centerline of the port for each layer of the flame burning.
Appliance manufacturers design gas appliances to have a stable burner flame by port
loading. Port loading is expressed as BTU per hour per square inch of open burner port
area. It is obtained by dividing the gas input rate by the total area of the port opening.
When enough primary air is introduced into a burner, a stabilized flame begins to form, and
the flame burns quietly. If too much air is introduced, or if the port loadings are increased,
the flame on the burner will have the tendency to lift (Figure 8-9). When the flames begin to
lift (blowing) off the burner, they become very noisy. If this condition persists, the flame cones
begin to rupture and complete combustion will not take place. In addition, the efficiency of
the gas burner begins to drop along with the BTUs and the appliance begins to lose its heat
content. If this condition is not corrected, aldehydes and carbon monoxide will begin filling
Additional flame-lifting possibilities include:
•Flame lifting is more likely to occur with natural gas appliances.
•Flame lifting will also occur if any operating or design factors cause the burner to
decrease the burning speed.
•If any operating or design factors increase the flow velocity from the ports, flame
lifting will occur.
•The port size and depth will affect flame lifting.
•Overrating the burners is a primary cause of flame lifting.
•A cold burner will cause the flame to lift, but it should settle down after a while.
Too much air supply
will cause the lames
to lift off the burner.
When the flame begins to ignite from within the burner head, a condition known as flashback
occurs. This is caused when the reduced flow velocity of the air-gas mixture is less than the
burning speed near the burner port. In other words, the inner flame cone becomes inverted
and ignites the gas from within the burner port. If the burner is properly adjusted, flashback
will not occur during normal operation of the gas appliance.
Additional flashback possibilities include:
•Flashback occurs in faster-burning gases.
•Flashback could occur when primary air is increased, which will increase the
•Flashback occurs with underrated burners with incorrect orifice size.
•Incorrect gas pressure will cause flashback.
•Decreased flow velocities from a burner port will cause flashback.
•Leaking burner valves cause flashback.
•Flashback can occur when a burner is first turned on if the air-gas mixture is too rich
or too lean.
When a burner is turned off, a condition known as “extinction pop,” or flashback on
extinction, could occur. This could happen immediately, or it may take a few seconds. The
extinction pop is caused by excessive air entering the burner when the gas burner valve is
turned off. The reduced flow rate of the normal air-gas mixture in a burner is replaced with
all air. In addition, it is possible for the flame speed to exceed the flow velocity of the gas,
causing a flashback. This condition is not hazardous—it is just annoying to the appliance
owner. With a burner that is properly designed, maintained, and adjusted, flashback will
not occur under normal operating conditions.
Yellow Flame Tips
In gas appliances, if the primary air supply is reduced, the inner cones of the flames will
begin to lengthen, and eventually they will disappear, turning the blue flame tips to yellow.
If the primary air supply is cut off completely, the flames will turn yellow (Figure 8-10).
When these yellow flames and glowing carbon particles impinge on a cool surface, they
begin to quench the complete combustion process and the carbon particles will not burn off.
In addition, carbon monoxide, soot, or both will begin to form when the yellow flames
impinge on a cool surface.
Dust particles in the air will begin to glow as they pass through a flame (Figure 8-11);
the flame’s appearance begins to have color streaks. These streaks will appear orangeyellow
and will not have an effect on complete combustion. The technician should not
confuse dust particles with yellow flame tips. True yellow flame tips will be a pale yellow
color and they can be eliminated by increasing the primary air supply. Depending on the
air conditions of the surrounding area near the gas appliance, when you increase the
primary air supply, you might also increase the amount of dust particles entering into
the flame. Another way to distinguish yellow flame tips from dust particles is to put on a
pair of brazing goggles and look into the flame. True yellow flame tips will not disappear.
The inner cone
the outer cone
in the mantle
Soot and yellow
tipping will appear
in severe cases
The flame lifted
off the burner
lifted off the
Normal blue flame Too much primary air
Not enough primary air Too much gas
Unburned air and
Unburned air and
FIGURE 8-10Characteristics of gas lames.
FIGURE 8-11Dust particles passing through a normal lame.
Mantle with dust
Inner cone Outer cone
Unburned air and
Appliance Burner Components
Over the years, appliance manufacturers have come out with many types of burner designs
(see Figure 1-1 in Chapter 1 and Figure 8-12). In fact, appliance burners must have the
•The burner design must be able to provide complete combustion of the gas.
•The burner design must provide for rapid ignition of the gas and be able to carry
over the flame across the entire burner.
•The burner must operate reasonably quietly during ignition, burning, and extinction
of the flame.
•The burner design must not allow for excessive flame lifting, flashback, or flame
•The burner must provide uniform heat over the heated area.
•Most important to the consumer and manufacturer, the burner must have a long
The gas orifice is not part of the burner, but it plays an important role in its operation
(Figure 8-13). In the service field, the gas orifice goes by many names, such as orifice hood,
spud, hood, or cap. The purpose of the gas orifice is to regulate or limit the flow of gas
into the burner. The size of the hole in the orifice will depend on what type of gas is in use
and what constant pressure is needed to light the
burner evenly. Another reason for use of an orifice is
to force primary air into the burner. Three types of
orifices that are in use are:
•The fixed orifice has a predetermined opening
in the orifice hood to allow a certain rate of gas
to flow (Figure 8-14).
•The adjustable orifice is mainly used in ranges.
This type of orifice will allow you to control the
gas rate, from zero to its maximum rated flow
•The universal orifice is also mainly used on ranges.
This type of orifice was designed to allow the range
to be operated on natural or liquefied petroleum
gas (Figure 8-16).
Most gas appliances that operate below the
elevation of 2000 feet may not need to have the orifices
replaced. If you have to replace the orifice, or if you
have to check to see if the correct orifice size is
installed, refer to Tables 8-1, 8-2, 8-3, and 8-4.
NOT E Gas appliances shipped from the manufacturer are set up for natural gas. If the home has LP
gas, then the appliance will have to be converted for LP use.
Gas oriices are used
to limit gas low to
FIGURE 8-14Different types of ixed oriices.
Type I Type II
Type IV Type V
Most gas appliances have an adjustable primary air shutter to adjust the air intake, and they
come in many designs. In addition, manufacturers have designed the air shutter to withstand
rust and corrosion and to be secured in any position (Figure 8-17).
When gas passes through an orifice, it enters the throat of the mixing tube (Figure 8-18).
Called the Venturi throat, this was designed to provide a more constant flow of primary air
into the mixing tube of the burner.
Fixed needle Movable needle
Adjustable orifice hood Fixed orifice hood
Orifice Drill Size
•A ventilation system will provide good air circulation and adequate oxygen supply
for the gas appliance and the occupants of the residence.
•It will remove the water vapors produced when burning gas.
A wide variety of venting options are available from vent manufacturers, and every gas
appliance manufacturer will provide venting instructions for properly installing its products. It
is strongly recommended that you follow these instructions. You must use the proper venting
materials as described in the installation instructions for the model being installed, and install
the venting system according to your local building codes. For additional information on
proper ventilation, visit www.epa.gov/iaq/homes/hip-combustion.html.
Troubleshooting Ventilation Problems
The most common problems with ventilation systems are:
•Improper maintenance of the ventilation system
•Incorrect sizing and installation of the ventilation system
•Inadequate air supply
If you suspect a problem with the ventilation system, check the following:
•Make sure that you have the correct vent sizing.
•Check if there are too many elbows or if the length of the venting system exceeds
the manufacturer’s recommendations or local building codes.
•Inspect the entire ventilation system for faults, such as a disconnected or crushed pipe.
•Inspect for an obstruction, such as a clogged vent cap.
•Inspect all air openings for obstructions.
Measuring Gas Pressure
When installing or repairing gas appliances, it is often necessary to measure the pressure of
the gas supply to the appliance. There also may be times when the technician will have to
test the gas pressures at the manifold or orifices. The two types of test instruments used
today to test the gas pressures are the manometer and the magnehelic gauge.
The manometer is a U-shaped tube equipped with a scale to measure gas pressure in water
column inches (Figure 8-21). Before you check the gas pressure on an appliance, locate the
model and serial number nameplate. This nameplate will have the gas rating stamped on it.
Now turn off the gas supply to the appliance. Before you can begin to test the gas pressure, you
must first set up the manometer by adding water to the U-shaped tube until both columns read
zero on the scale (Figure 8-22a). If reading the scale is difficult, you can add a food coloring to
the water to enhance the color so that you can read the scale better. When measuring gas
pressure in an appliance, the tubing from the manometer is attached to the orifice, manifold, or
gas supply line, and the other end of the tube on the manometer is left open to the room
atmosphere. To test the gas pressure at the burner orifice, remove the burner (Figure 8-23).
Next, attach the long hose from the manometer to the burner orifice. Now turn on the gas
supply to the appliance. In addition, turn on the burner valve being tested, and turn on one
other burner to serve as the load. When the gas pressure is applied to the manometer, it pushes
down on the water column and the water column rises
on the other side of the manometer (Figure 8-22b). To
read the manometer scale, observe where the water
column stops. In Figure 8-22b, the incoming gas has
pushed the water in the manometer down 2 inches
below zero, and the water column on the other side is
pushed up 2 inches above zero. The pressure reading is
obtained by adding the two readings together. Figure
8-22b shows that the total change equals a 4-inch water
column. The reading should be within the rating on the
model and serial nameplate.
The magnehelic gauge shown in Figure 8-24 also
measures gas pressure. This gauge can measure gas
pressure faster than the manometer can. To use this
type of gauge, just follow the same procedures for the
manometer. The only difference is that you read the
gas pressure directly from the gauge scale. Some
models have different scales on the gauge dial—just
read the gauge that indicates water column pressure.
Many companies manufacture test instruments for
checking gas pressures. Websites to check out include:
Testing for Gas Leaks
When testing for a gas leak, do not use a lighter or a
lit match. That is not the safe or correct way to test for
gas leaks. All gas appliances, when they are installed
or repaired, must be tested for leaks before placing
the appliance in operation. Remember, LP or LPG gas
is heavier than air and settles in low-lying areas. If
you do not have a combustible gas detector (and I
recommend that you purchase one), use your nose to
smell for a gas leak all around the appliance at floor
level. A safe and effective way to test for gas leaks is
to use a chloride-free soap-and-water solution to
check all connections and fittings. The solution can be
sprayed, applied directly, or an applicator can be used
to spread the solution. If a gas leak is detected by the
soap solution it will begin to form bubbles.
Sometimes, air might be present in the gas lines
from installation or repairs, and it could prevent the
pilot or burner from lighting on initial startup. The gas
A manometer. This
instrument is used to
test gas pressure.
lines should be purged of air in a well-vented area. Before proceeding with purging the gas
lines, inspect the work area for any other sources of ignition, such as flames, burning candles,
running electrical appliances, etc. With a safe working environment, you can begin to purge
the gas lines. On gas ranges/ovens, just turn on the burners until you smell the gas or until
the burners are lit properly. With gas dryers and gas water heaters, turn off the gas supply
valve. Remove the gas line from the appliance, and slowly begin to turn on the gas supply
valve. When you begin to smell gas, turn off the main supply valve. Next, reconnect the gas
line to the appliance, open the gas supply valve, and test for gas leaks. If there are no gas
leaks, run the appliance.
Use an approved pipe joint compound for connecting gas piping and fittings to the
appliance. In addition, never use white Teflon tape on gas lines. White Teflon tape does not
guarantee a leak-free connection. You can use a PTFE yellow Teflon tape on gas connections
and fittings. This type of approved Teflon tape is a specially designed thread-sealing tape
for use on gas appliances. To attach PTFE yellow Teflon tape to pipe thread, wrap the tape
in the direction with the thread, as shown in Figure 8-25.
Combustible Gas Detector
Combustible gas detectors are another general-purpose tool that the service technician
could use to detect gas leaks (Figure 8-26). This instrument uses an audible alarm that gets
louder when you approach a gas leak. This device has the capabilities of detecting LP
(LPG) or natural gas and other hydrocarbons and halogenated hydrocarbons, depending
on the manufacturer. The sensitivity of a combustible gas detector can be between 50 and
1500 ppm of gas detection, with an instantaneous response.
One manufacturer of combustible gas detectors can be viewed on the Web at www
Gas Conversion Procedures
Before installing a new gas appliance, look at the model and serial dataplate to determine
that the appliance is made for the type of gas supplied in the home. Do not install an LP or
LPG gas appliance when natural gas is supplied to the home. Conversely, do not install a
natural gas appliance when LP or LPG gas is supplied to the home.
Appliance manufacturers do make gas appliances that can be installed with either LP or
natural gas. All you have to do is follow the manufacturer’s recommendations for converting
the appliance from one type of gas to the other.
Gas Pressure Regulator
To convert a gas pressure regulator from one type of gas to the other, you must first shut off
the main gas supply to the appliance (Figure 8-27). Also, if the gas range has an electrical
connection, turn off the electricity. Locate the gas pressure regulator valve. On some models, the
gas pressure regulator valve is located in the lower rear of the range (Figure 8-28a) or under the
cooktop (Figure 8-28b). To convert the gas pressure regulator valve, you do not have to
remove it from the range. Just gain access to it. As you can see in Figure 8-29, remove the
plastic cover from the regulator cap. Next, unscrew the gas pressure regulator cap with a
wrench; turn it counterclockwise to remove the cap and leave the spring in the regulator.
NOTE In Figure 8-29, the regulator cap has a gas designation stamped on it.
For LP gas operation, the “<-LP” indicator must face in the direction of the gas pressure
regulator, and the hollow end faces away from the regulator. For natural gas operation, the
“<-NG” indicator must face in the direction of the regulator, with the dimple end facing
away from the valve. Reinstall the cap and tighten with a wrench in the clockwise direction.
Do not overtighten the cap, as you might damage it. Finally, replace the plastic cover on the
Converting Surface Burners
To convert the surface burners from one type of gas to the other, you must first shut off the
main gas supply to the appliance (see Figure 8-27). Also, if the gas range has an electrical
connection, turn off the electricity. Remove the burner grate and burner cap (Figure 8-30).
Remove the screws from the burner base, and reinstall one screw to hold the orifice holder
(Figure 8-31) secured to the cooktop. This will steady the orifice holder so that you can
remove the orifice without damaging the orifice holder. To remove the orifice, use a 5/16 nut
driver with masking tape applied to the end of it. The masking tape will hold the orifice in
the nut driver when you remove it. Turn the nut driver counterclockwise to remove the
orifice. Locate the extra orifices that came with the range. Most likely, they will be attached
Converting the Bake/Broil Thermostat
Gas ranges with oven pilot lights will have to be converted from one type of gas to the other.
Remove the oven thermostat knob to expose the oven thermostat selector. Insert a small
screwdriver into the pilot control screw, turn the screw clockwise for LP or LPG gas or
counterclockwise for natural gas (Figure 8-35). Replace the oven thermostat knob. Gas ranges
with electronic spark ignition for pilot control will be discussed later in the book.
Gas Appliance Maintenance
To maintain gas appliances, always follow the manufacturer’s recommendations for periodic
maintenance as stated in the use and care manual. The range, oven, or cooktop can be cleaned
with warm water, mild detergent, and a soft cloth on all cleanable parts, as recommended in
the use and care manual. Also, never use abrasive cleaners that are not recommended by the
Do not allow grease spillovers to accumulate after cooking on top of the range; it will
become a fire hazard. When cleaning the burners, always make sure that all of the portholes
are free of debris. If, for any reason, the burner portholes are blocked, the flame appearance
will be different. Blocked portholes will reduce gas flow, and the heating value of the burner
will be reduced. Maintenance procedures for gas water heaters and gas dryers will be
discussed in later chapters.
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