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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.

Gas Safety

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

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

that product.



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

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





The combustion


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 and

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 1.98.6

Amount of air required to burn 1 cubic foot of gas Cubic foot 23.86 31.02

Ignition temperature in air °F 9201020 9001000

Maximum lame temperature in air °F 3595 3615

Octane number












100 Over 100 92

All data are approximate.

FIGURE 8-2 Properties 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,

oxygen, carbon

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

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

carbon dioxide.

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.

The “Flame”

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

Outer mantle

Incandescent products

of complete combustion

Outer cone

Complete combustion of

intermediate products

Inner cone

Zone of partial combustion

Unburned mixture of gas

and primary air

Gas orifice

Burner port



Primary air


Primary air


Orifice spud

Gas supply

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,

and hydrogen.

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 8-7 Different lame types of a Bunsen burner, depending on the amount of oxygen supplied.


Inner cone

Unburned air and

gas mixture

Outer cone


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.

Air Supply

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.

Flame Appearance

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.

Flame Lifting

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

the room.

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

burning speed.

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.


Inner cone



The inner cone

pushed through

the outer cone

Yellow tipping

in the mantle


Outer cone

Soot and yellow

tipping will appear

in severe cases


Outer cone

The flame lifted

off the burner

The flame

lifted off the


Normal blue flame Too much primary air

Not enough primary air Too much gas

Outer cone



Unburned air and

gas mixture

Inner cone

Unburned air and

gas mixture



FIGURE 8-10 Characteristics of gas lames.

FIGURE 8-11 Dust particles passing through a normal lame.

Mantle with dust


Inner cone Outer cone

Unburned air and

gas mixture

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

following features:

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

service life.

Gas Orifice

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

(Figure 8-15).

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 8-14 Different types of ixed oriices.






Type III

Type I Type II

Type IV Type V

Air Shutter

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).

Venturi Throat

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.



Gas Gas

Fixed needle Movable needle

Adjustable orifice hood Fixed orifice hood


Orifice Size

Drill Size

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

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

regulator cap.

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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