Gas Flame Characteristics
By observing the flame pattern on a gas
furnace the experienced technician can tell a
lot about what is going on in the furnace and
the gas supply.
The shape, the color and the pattern of the
flame are all things to keep in mind.
By observing how furnaces run correctly you
can tell what is wrong with a furnace. Which
is why most new technicians spend time
doing preventative visits before service calls.
Types of problems
Types of flame:
Flame to small
Flame lifts off the burner a little bit.
It is a turbulent an noisy flame
Can cause carbon monoxide
Caused by too much primary air, too large of a
burner orifice, too high of gas pressure.
Causes combustion too occur inside the burner
Flame will come out the wrong end of the burner
tube, almost like a roll
Caused by low manifold pressure, too much
primary air, dirty burner orifice, dirty burners, low
gas supply pressure.
This is a yellow tipped flame.
Can cause carbon monoxide and soot buildup.
Caused by inadequate primary air (too little), dirty
burner orifices, restricted heat exchanger,
restricted vent system.
This flame waves around, is not steady and is a
lazy appearing flame.
Caused by insufficient secondary air, restricted
heat exchanger, and air blowing flame through
May be sign of a cracked heat exchanger.
The flame is going in the wrong direction through
the burners and heat exchangers.
Caused by a restricted heat exchanger, blocked
vent system, inadequate primary air, high gas
Flame too small
Flame is just too small, may not be heating the
This can be caused by low gas manifold pressure,
dirty or blocked burner orifice, or the burner orifice
may be too small (DO NOT ADJUST ORIFICE
SIDE WITHOUT CHECKING WITH
MANUFACTURER TECHNICAL SUPPORT!)