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

Page: 28 / 92

Fig. Twister water heater
2
3
1
1. Water inlet
2. Heat exchanger
3. Water outlet
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.
28 Installation, Maintenance and Service part