A.O. Smith 120 trough 500 User Manual

Page 17

BTR TANK TYPE HEATERS

SERVICE HANDBOOK

A.O. Smith Water Products

Service Handbook

Training Department

BTR 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 BTR 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, de-
energizing 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 satisfie’s, main
and pilot gas is shut off.

9. Flue damper closes