Bradford-White Corp U4TW50T*FRN Sequence of Operation, Power Up Sequence, Normal Heating Sequence

Sequence of Operation

Power Up Sequence

1.Start-up: Upon power up, the gas control runs a safe start check with a typical delay of 5 seconds.

2.Flammable Vapor Verification: The gas control verifies that the Flamma- ble Vapor Sensor is in the proper operating range prior to energizing any components. If the sensor is within the proper range, the gas control resumes normal operation. If the Flammable Vapor Sensor is out of range, the gas control LED immediately flashes 7 times with a 3 second pause.

Normal Heating Sequence

1.Thermostat Calls for Heat: Prior to energizing the blower, the gas control checks the safety circuit to insure the circuit is open. In the safety circuit the pressure switch is normally open and the blower temperature switch is normally closed.

2.If the safety circuit is closed, the gas control waits 4 seconds, the gas control LED flashes 2 times with a 3 second pause. The gas control waits 2 minutes. Then, the blower runs for 30 seconds. This cycle re- peats until the safety circuit opens.

3.Blower energizes.

4.Pressure switch proves blower/vent system operation: If the pressure switch does not close within 30 seconds, the gas control LED flashes 3 times with 3 second pause. The blower runs for 30 seconds every 2 min- utes trying to get the pressure switch or blower temperature switch to close. This cycle repeats as long as there is a call for heat.

5.Blower pre-purge period (15 seconds).

6.Trial for Pilot Ignition (90 seconds): The gas control lights the pilot by activating the spark igniter and gas flow to the pilot burner. If flame is not sensed within 90 seconds, the spark igniter and gas flow are deacti- vated. The blower will post-purge, and the gas control LED flashes 6 times with a 3 second pause.

Page 12

12