Bradford White D4403S series Manual page 30

Troubleshooting continued-
Control Sequence of Operation
Start up Sequence
Upon powering up, the control checks for the presence of the flammable
vapor sensor, if the resistance is in the expected range the control will begin
normal operation after 5 to 8 seconds.
Normal Heating Sequence
1. The thermostat senses a need for heat.
2. The damper test circuit checks the position of the damper.
3. If the damper is open, and starts the ignition process by providing a spark
at the pilot electrode and allowing gas to flow to the pilot.
4. When the pilot is lit the gas control senses the pilot flame and opens the
main gas valve.
5. The main burner is lit.
6. The main burner (damper in open position) continues to operate until the
thermostat is satisfied.
7. When the thermostat is satisfied the main and pilot gas valves close.
8. The damper remains open for a short period before closing.
The water heater remains in the stand-by mode until the next call for heat.
30