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1. Thermostat calls for heat
7. Thermostat satisfies
3. Intermittent
Ignition Control
5. Main gas valve opens
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.
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.
Technical Training Department
Ashland City, TN ©2003
SBD TANK TYPE HEATERS
SERVICE HANDBOOK
SBD SEQUENCE OF OPERATION
16
2. Flue damper opens
6. Main burner ignites
Once the pilot flame is established and
9. Flue damper closes
4. Pilot gas opens,
Pilot sparks and
flame proves
8. Main and pilot
burners "OFF"
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