American Standard ULN80-125 Operation, Installation And Service Manual page 25

Verify Pilot Ignition by using Flame Sensor. Ignition of pilot gas is verified by a flame sensor.The flame sensing electrode is locat-
ed in the pilot flame pattern and through a flame rectification process verifies that a correctly sized pilot flame exist. This causes shut off
of the spark circuit and opens the main gas valve.
Main Gas Valve. When the flame sensor verifies an adequate pilot flame igniting sparks are shut off and the main gas valve opens
allowing gas flow to the main burners. Main burner gas is ignited by the pilot burner. The pilot burner is an intermittent type device and
remains lit for the duration of the burn cycle.
Electronic Control satisfied (Temperature sensor & potentiometer). This action opens the electric circuit to the gas valve.
The flue damper motor is energized to turn the damper to the closed position (WHEN APPLICABLE),the combustion air blowers shuts off.
Power Failure of interrumption. The gas valves, which are held open by electromagnetic coils, close, shutting off all gas flow.
Restoration of power initiates the sequence of operation from the beginning.
Loss of Flame Sensing. On loss of pilot flame or loss of flame sensing (burned off electrode, broken sensor lead), the ignition module
shuts off main gas flow and immediately re-starts the pilot ignition sequence while maintaining operation of the combustion air blower and
holding the flue damper in the open position. If the pilot flame can be re-stablished within 90 seconds, the normal operation sequence will
be resumed. On loss of flame sensing due to shorting of the flame sensor lead, the ignition module shuts off main gas and unless the short
is correct within 90 seconds, the ignition control will lock out and manual restart will be required after the shorting problem is fixed.
Lockout and Continuos Retrail for Ignition. The ignition module is designed to lock out operations if the pilot burner cannot
be ignited within 90 seconds from the start of the ignition sequence. In order to prevent property damage (winter freeze-up as an
example) and when the failure for the pilot to ignite is due to possible utility problems, (low gas pressure, low line voltage, rolling
blackouts etc.) the ignition module will try to restart operation of the unit continuosly every hour until operation is restored (after power
loss is restored)
WARNING
TO AVOID POSSIBLE INJURY. FIRE AND EXPLOSION, READ THESE PRECAUTIONS BEFORE ATTEMPTING TO LIGHT OR
RELIGHT THE PILOT. Check the rating plate near the gas control thermostat for correct gas. DO NOT USE THIS WATER HEATER
WITH ANY GAS OTHER THAN THE ONE LISTED ON THE RATING PLATE (Figure 5). Failure to use the correct gas can cause
problems which result in DEATH, SERIOUS BODILY INJURY, OR PROPERTY DAMAGE. If you have any questions or doubts consult
your gas supplier or gas company.
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