Trouble shooting
14
BURNER PROBLEMS
LIFTING BURNER FLAMES:
Excessive primary air can cause flames to lift and blow off the burner ports which can be noisy as well as
inefficient. More importantly however is the production of dangerous carbon monoxide under this
condition. Any factor which reduces burning speed promotes lifting flames. Also, any factor which
increases flow velocity from ports contributes to lifting flames. Overrating of burners is also a cause. The
normal cure for lifting flames is the reduction of primary air input to the burner.
FLASHBACK:
Flashback occurs when gas-air flow velocity is less than burning speed at some point near a burner port.
Flash back is a condition where gas ignites within the burner. Any factor which increases burning speed
tends to promote flashback, and any factor decreasing flow velocity from the ports will contribute to
flashback. Flashback is more prevalent with faster burning gases. Natural gas is relatively slow burning
gas hence flashback is less likely. Reducing primary air is the usual cure for flashback.
EXTINCTION POP:
This is merely flashback occurring when a burner is turned off. It is usually instantaneous although it can
occur several seconds after the burner has been turned off. What happens is that primary air continues
to flow into the burner even though the gas jet has been cut off and does not inject air. The mixture in
the burner changes from the normal operating mixture to all air and flow rate through the ports falls off
toward zero. Under these conditions, it is possible for the flame speed to exceed flow velocity at some
instant and flashback may occur. The result is a tiny explosion or pop. Since increasing primary air
increases the burning speed, it is obvious that reducing primary air input will reduce the flashback
tendency.
YELLOW TIPPING OF FLAMES:
Too severe a reduction in primary air also causes its problems. Yellow tipping is one of them. Flames will
eventually become all yellow if no primary air is supplied. These yellow tips are caused by glowing carbon
particles in the flame. Soot will form if these yellow flames impinge on cooler surfaces. Here again
carbon monoxide can be produced. Yellow tipping is corrected by the injection of more primary air.
FLUCTUATING FLAMES:
Length of burner flames may fluctuate or shorten over a period of time with no re-adjustments of the
burner. This condition usually indicates a non-uniform gas pressure at the orifice. Fluctuating flames
usually do not create any immediate problems, such as incomplete combustion, unless flames impinge on
cool surfaces. This condition should be corrected, however, since it warns of possible future problems.
Unsteady gas pressures cause flames to fluctuate. Usually this condition indicates problems with the gas
pressure regulator, the gas meter or other gas supply problems. Check the orifice for blockage by dust or
dirt from supply lines. Very small pilot orifices are quite prone to blockage. Occasionally, too much
grease in pilot valves restricts gas flow to pilot burners. Remove any excess greases.
FLAME ROLLOUT:
When the condition known as flame rollout occurs, flames roll out of the combustion chamber openings
when the burner is turned ON. Flame rollout may create a fire hazard, or scorch appliance finishes, burn
wire, or damage controls. The gas in the burner mixer may be ignited, producing flashback. Flame rollout
is actually a variation of floating flames, with flames reaching for air outside the combustion chamber.
Again, the basic cause is a lack of combustion air. This lack of air may be due to overrating of burners,
poor draft or blockage of flueways. Apply the corrections for these problems listed for floating flames.
Some appliances use step-type controls. These controls limit initial gas flow to the burner to establish
natural draft in the appliance before full gas rate is allowed to flow. Check the operation of this control,
and replace the control if it is faulty.
