A.O. Smith TWI 35-200 Installation, User And Service Manual page 28

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Fig. Twister water heater
When the temperature is too low, the water heater starts a operating cycle:
1. The controller detects a "heat demand".
2. The fan starts pre-purging.
3. The air proving switch closes when the air pressure differential is sufficient.
4. The spark plug is activated.
5. The gas control valve opens and the gas/air mixture is ignited.
6. The water heater heats the water in the tank.
7. When the water temperature reaches the setpoint, the heat demand ends and the
controller stops the operating cycle.
8. The fan starts post-purging.
The operating cycle starts again when a new heat demand is detected.
1. Water inlet
3
2. Heat exchanger
3. Water outlet
2
1
Installation, Maintenance and Service part