Operating Principles GL16
5-10
Flame Safeguard
The solid state electronic flame safeguard
(FC1) provides primary protection for gas system
operation. The flame safeguard receives its
electric operating power as long as the unit is
operating and the front panel GAS switch is set
to ON.
The flame safeguard makes sure the flame is
established in the burner and that it is safe to
continue supplying gas to the burner. It provides
pre-purge and post-purge timing for the
combustion blower.
Inputs to the Flame Safeguard
The flame safeguard monitors input signals
from the safety interlock circuit, combustion air
pressure switch, and UV flame scanners.
Safety Interlock Circuit
Initiates the flame safeguard’s sequence
of operating the burner only when all of
the controls in the circuit are satisfied and
the INTERLOCKS CLOSED green LED
on the flame safeguard is lit.
For more information within this section
on components in the safety interlock cir-
cuit, go back to the
Safety Interlock
Circuit section.
Combustion Air Pressure Switch
(PS1) must be open before the combus-
tion blower operates and before any elec-
tric gas valve is opened. If this pressure
switch is already closed when the flame
safeguard attempts to turn on the com-
bustion blower, the flame safeguard will
lockout and the SYSTEM ERROR red
LED on the flame safeguard will come
on.
UV Flame Scanner Circuits
These circuits are routed in separated con-
duits from the other electrical wires.
The yellow common lead wires for each
scanner are connected together and to ter-
minal S2 of the flame safeguard.
The relay (CR5) in the flame safeguard
mounting base switches between the blue
hot lead wires for each scanner.
• When relay CR5 is energized, the pi-
lot UV flame scanner (UV1) in the
left end frame is connected to termi-
nal S1 of the flame safeguard.
• When relay CR5 is NOT energized,
the end of burner UV flame scanner
(UV2) in the right end frame is con-
nected to terminal S1 of the flame safe-
guard.
Outputs from the Flame Safeguard
The outputs from the flame safeguard provide
signals to the pilot gas valve, ignition transformer,
primary burner gas valve, and the combustion
blower.
In the event of a flame failure, an alarm signal
from the flame safeguard shuts down the gas
operation. The flame safeguard must be reset
before another start-up is attempted.
Pilot Valve and Ignition Transformer Circuit
Energizes both the pilot gas valve and the
ignition transformer at the same time.
Circuit is energized for sufficient time to
light the pilot and the main burner. If the
PILOT TEST/RESET button on the flame
safeguard is in the IN position, only the
pilot valve and ignition transformer will be
energized.
Main Gas Valve Circuit
Energized only after the pilot flame is
proven and thereafter only when the main
flame is sensed. If flame is not detected
continuously for 3 seconds, this circuit is
disconnected.
Combustion Blower Circuit
Energizes the combustion blower motor
contactor before, during, and after the
burner circuit is energized for a predeter-
mined time.
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