IM 685 / Page 11
Flame Start-up
1. Open the gas line cocks and position switch S3 to AUTO. The flame safeguard will go through the
10 second "Initiate" period, after which the burner motor will start. The modulating air and gas
valve actuator VM1 will drive the air valve to the full open position. At full open the 60 second
prepurge period will begin. After 20 seconds at maximum open, the actuator will begin a 30 second
stroke to reposition the air valve back to the minimum position. Upon completion of the 60 second
prepurge cycle, gas valve GV1 will open (as indicated when the LED marked PILOT comes on), the
ignition transformer is powered and the flame should come on at minimum rate.
2. Observe the gas manifold pressure manometer during this sequence. The manifold pressure should be
close to zero (it will indicate a slight heat exchanger pressure caused by the burner combustion air
fan). When gas valve GV1 opens it should indicate a manifold pressure approximate to the values
listed in Table 5, Column 10. Approximately 3 seconds after GV1 is powered the flame will come on
and the flame signal will read 1.5 to 5.0 volts DC. The LED marked FLAME will come on when
flame is detected and the LED marked MAIN will come on if flame is being detected at the end of
the 10 second trail for ignition period. When the LED marked MAIN comes on gas valves GV4-
GV8 (when included) will also open and the firing rate will be determined by the control system. On
the initial start-up if the flame does not light and the flame safeguard locks out, reset it and make
several attempts to light before assuming there are problems other than more air in the gas lines. If
initial flame operation is erratic wait until after a period of main flame operation has further purged
the gas lines before trying to "adjust out" something that may actually be caused by air in the lines.
Modulate Firing Rates
Set the temperature control system so the burner actuator VM1 will modulate to increase the firing rate.
Observe the flame signal and the manifold pressure manometer as this is occuring. The flame signal
should remain between 1.5 to 5.0 volts DC through the entire range of the burner, and the manifold
pressure should be between the values indicated by Table 5, Column 9 and 10. If the manifold pressure
shoots above these values and then slowly returns to normal as the burner is modulating down to a
lower firing rate, isolate which combination gas control is causing this. Check that valves pressure
regulator adjustment per “Gas Valve Pressure Regulator Adjustment” section. If this condition cannot
be adjusted out, replace the valve. If combustion appears normal, proceed with the combustion test.
Combustion Tests
These tests should be run when the furnace is at normal operating temperature (after the furnace has
been running 10 to 15 minutes), and should be run at several firing rates including maximum and
minimum.
a. Check input: See Verify Input Rate
b. Check CO
2
: See Check CO
2
, CO & Stack Temperature
c. Check CO: See Check CO
2
, CO & Stack Temperature
Cycle the Unit
Cycle the unit through several start-ups with the temperature controls calling for first minimum rates
and finally maximum rates. Be alert for any hints of trouble or unexplained inconsistencies that could
indicate future problems.
Record Data
After the gas burner has been successfully started up, checked out and is operating correctly, readings
should be taken and recorded for future reference (see Table 6). If problems develop in the future,
variations in these readings will indicate what has changed and where to start looking for problems.
