Sequence Of Operation; Lighting & Operation Label - A.O. Smith BTR 151 Instruction Manual

The following information will describe the Sequence of Operation
for this appliance.
1. Switch power on to unit.
2. Thermostat calls for heat.
3. Ignition Control Board performs diagnostic check on system
components.
4. On completion of diagnostics check, the Ignition Control Board
sends signal to Exhaust Inducer.
5. Exhaust Inducer begins drawing air through appliance closing
the Prover Switch.
6. On completion of Prover Switch engagement, the Ignition
Control Board begins the ignition cycle.
7. The Ignition Control Board provides power to the Silicon
nitride Igniter.
8. The Silicon nitride Igniter heats up for approximately 17 to
20 seconds.
9. At the end of Silicon nitride Igniter's warm-up, the Ignition
Control Board opens the gas Valve.
lighting & operation laBel

seQuence of operation

figure 22.
25
10. From the time the gas Valve opens, the Ignition Control Board waits
3 seconds and then shuts off power to the Silicon nitride Igniter.
11. From the time the Silicon nitride Igniter's power is shut off,
the Ignition Control Board waits 3 more seconds to monitor
the Flame Sensor.
12. If the Flame Sensor does not detect a strong enough flame,
the Ignition Control Board shuts off the gas Valve and allows
the Exhaust Inducer to purge the unit for 20 seconds. At that
time, the Ignition Control Board restarts with step 7. It will try
and ignite the main burners 2 more times. If the unit does not
light, the Ignition Control Board will wait one hour and then
restart at step 3. This cycle will continue until the unit lights or
the power is shutoff to the unit.
13. If the Flame Sensor detects a strong flame, the Ignition Control
Board will allow the unit to operate until the thermostat is satisfied.
14. Once the unit is satisfied, the Ignition Control Board will shut
off the Gas Valve and the unit will be in standby mode until
another call for heat is initiated by the thermostat.
See the flow chart on page 26 for more information.