Figure 33.
Flame characteristics of properly-adjusted
natural gas systems
Burner flame at startup: 1.2-in. WC manifold pressure
draft inducer—high speed
Burner flame at high fire: 3.5-in. WC manifold pressure
draft inducer—high speed
Startup
OAU-SVX01K-EN
53
Main Burner Flame
•
The burner flame should be predominately blue in
color and well defined and centered at the tube
entry as shown in
above. Distorted flame
or yellow tipping of natural gas flame, or a long
yellow flame on propane, may be caused by lint and
dirt accumulation inside burner or at burner ports,
at air inlet between burner and manifold pipe, or
debris in the main burner orifice. Soft brush or
vacuum clean affected areas.
•
Poorly defined, substantially yellow flames, or
flames that appear lazy, indicate poor air supply to
burners or excessive burner input. Verify gas
supply type and manifold pressure with rating
plate.
•
Poor air supply can be caused by obstructions or
blockage in heat exchanger tubes or vent discharge
pipe. Inspect and clean as necessary to eliminate
blockage. Vacuum any dirt or loose debris. Clean
heat exchanger tubes with stiff brush. Poor flame
characteristics can also be caused by flue gas
recirculation into combustion air supply. If
surrounding buildings or prevailing winds cause
recirculation, a flue extension may be required to
prevent recirculation. Contact manufacturer prior
to making any flue adjustments.
•
Reduced air delivery can also be the result of
inducer fan blade slippage, dirt accumulation in the
fan blade or low voltage to draft inducer motor.
Inspect draft fan assembly and be sure fan blade is
secure to motor shaft. Check line voltage to heater.
7. Flame Sensor Current Check
NOTICE
Meter Damage!
Measuring voltage with meter connect to a circuit
could result in meter damage. Do NOT measure
voltage with meter connected to a circuit.
Flame current is the current which passes through the
flame from the sensor to ground. A flame signal of 0.5
to 1.0 microamp (
A) is marginal. For dependable
operation, a flame signal of greater than 1.0
A is
required. To measure flame current, connect a meter
capable of reading micro-amp current so the flame
signal will be read thru the meter’s COM and
A
connections. The meter should read greater than
1.0
A.
Note: If the meter reads below “0” on scale, meter
leads are reversed; disconnect power and
reconnect meter leads for proper polarity.
Figure 34.
OAK/OAN indirect fired gas furnace components
