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SBD TANK TYPE HEATERS
SERVICE HANDBOOK
Technical Training Department
Ashland City, TN ©2003
16
SBD SEQUENCE OF OPERATION
1. Thermostat calls for heat
2. Flue damper opens
3. Intermittent
Ignition Control
5. Main gas valve opens
7. Thermostat satisfies
4. Pilot gas opens,
Pilot sparks and
flame proves
6. Main burner ignites
8. Main and pilot
burners "OFF"
SEQUENCE OF OPERATION
To understand SBD tank type water heaters, an examination of their sequence of
operation is necessary.
When the thermostat calls for heat, the relay in the draft hood assembly activates the
flue damper motor. The damper opens and power flows to the IID (Intermittent
Ignition Device). This activates the IID module to open the pilot valve and begin
sparking at the pilot burner assembly. Once the pilot flame is established and
confirmed back to the IID, the sparking is stopped and the main gas valve is opened,
allowing gas flow to the main burner. When the thermostat satisfies, main and pilot
gas is shut off. Damper is returned to closed position.
9. Flue damper closes