13. Prior to completing the start-up, check the appear-
ance of the main burner flame. See Figure K12 and
Figure K13 for flame characteristics of properly ad-
justed natural gas systems.
a. The burner flame should be predominantly blue
in color, well defined and centered at the tube
entry. Distorted flame, 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 be-
tween burner and manifold pipe, or debris in the
main burner orifice. Soft brush or vacuum clean
affected areas.
b. 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.
c. Poor air supply can be caused by obstructions
or blockage in heat exchanger tubes or vent dis-
charge pipe. Inspect and clean as necessary to
eliminate blockage. Vacuum any dirt or loose de-
bris. Clean heat exchanger tubes with stiff brush.
Poor flame characteristics can also be caused by
undersized combustion air openings or flue gas
recirculation into combustion air supply. Increase
air opening size or re-direct flue products to pre-
vent recirculation.
d. Reduced air delivery can also be the result of 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 se-
cure to motor shaft. Check line voltage to heater.
Shut Down
1. Set thermostat or controller to lowest setting.
2. Turn off electrical supply to unit at disconnect switch.
3. Turn off manual gas supply.
4. Disconnect manifold and inlet pressure taps and re-
install pipe plugs.
5. Replace vestibule access panel or close door.
Normal Operation
1. Turn on electrical supply to unit at disconnect switch.
2. Turn on manual gas supply.
3. Set thermostat or temperature controller to desired
temperature.
4. Information outlining the normal Sequence of Op-
eration and Wiring Diagram for the control system
supplied with the furnace model is enclosed with this
instruction.
Figure K13: Burner flame at high fire 3.5” w.c.
manifold pressure draft inducer – high speed
Figure K12: Burner flame at start-up 1.2” w.c.
manifold pressure draft inducer – high speed
FC−
FC+
Multi-purpose meter
Use microamp scale
Red (+)
Black (−)
Series 35-61 Module
Figure K14: Flame sensor current check
VCES-VHC-IOM-1F – VHC-36, -42 & -50
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