A.O. Smith BTR 201, Service Handbook

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Servicing should only be performed by a Qualified Service Technician
BTN/ BTR 151, 201 – ELECTRICAL SEQUENCE
The following information will describe the Sequence of Operation for this water heater:
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 the water heater 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.
10. From the time the Gas Valve opens, the Ignition Control Board waits 3 seconds and then shuts of
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.