Bradford-White Corp U4TW40TFRN, U4TW50TFRN Normal Heating Sequence cont’d, Abnormal Operation

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Sequence of Operation

Normal Heating Sequence (cont’d)

7.Main Burner Ignition: After pilot flame is sensed, the gas control acti- vates the main valve for main burner ignition. The gas control will ig- nore flame and pressure switch signals for 3 seconds to allow for the main burner to stabilize.

8.Steady State Operation: During steady state operation, the gas control monitors:

Thermostat Temperature Sensor: When the setpoint temperature is sat- isfied, the gas control is shutdown, and the blower will post-purge for 15 seconds. The gas control LED flashes a short flash once every 4 seconds (Idle status code).

Pressure switch/blower temperature switch: If either switch opens, the pilot valve and the main valve are shut down. The blower continues to run for 30 seconds attempting to close the circuit. The gas control LED flashes 3 times with 3 second pause.

Flame Sensor: If flame is lost, the pilot and main valves are shutdown. The blower runs for 15 seconds. The gas control attempts to re-light the pilot 4 times. If unsuccessful, the blower is shutdown, and the gas con- trol proceeds to a 5 minute lockout. The gas control re-attempts to light the pilot starting at Normal Heating Sequence #2.

9.Thermostat Satisfies: Gas control LED flashes once every 4 seconds. 10.Burner Off.

11.Blower post-purge (15 seconds).

Abnormal Operation

1.Flammable Vapor Sensor Fault:

A)If the resistance is greater than 70,000 ohms: The gas control imme- diately turns off all outputs. The gas control waits and monitors resis- tance for 30 seconds. If the resistance is greater than 65,000 ohms af- ter 30 seconds, the gas control proceeds to verify resistive delay for 2 minutes and flashes 7 times then 1 time with a three second pause. This process is repeated 5 times until the control either returns to normal op- eration or proceeds to flammable vapor lockout.

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Contents Service Manual Table of Contents Page Page Introduction Bradford White ECO-DEFENDER Safety SystemHow the Safety System Works How to Use this ManualTools Required Tools Required for ServiceSpecifications Gallon Vent TablesSpecifications Control Timings Wiring DiagramSequence of Operation Power Up SequenceNormal Heating Sequence Abnormal Operation Normal Heating Sequence cont’dAbnormal Operation cont’d Sequence of Operation Sequence of Operation LED Status Control Status Probable Cause Service Procedure TroubleshootingTroubleshooting Troubleshooting Burner Cleaning Procedure Burner MaintenanceBurner Inspection Burner Cleaning Procedure cont’d Pilot Inspection, Testing and Replacement Pilot MaintenancePilot Inspection, Testing and Replacement cont’d Page Pressure Switch Testing Pressure Switch TestingPressure Switch Testing cont’d Pressure Switch Replacement Pressure Switch ReplacementBlower Testing Blower TestingPage Blower Installation Blower ReplacementBlower Removal Blower Installation cont’d Blower Temperature Switch TestingBlower Temperature Switch Testing Switch Setting Blower Temperature Switch Testing cont’dBlower Temperature Switch Replacement Blower Temperature Switch ReplacementThermal Well Testing Thermal Well TestingThermal Well Testing cont’d Determine Tank TemperatureDetermine Water Temperature Inside Tank Sensor Resistance at Various Temperatures Component DisassemblyGas Control & Thermal Well Removal From Water Heater Gas Control Removal Gas Control Assembly to the Thermal Well Gas Control AssemblyGas Control Removal From Thermal Well cont’d Gas Control Assembly to the Thermal Well cont’d Flammable Vapor Sensor Testing Flammable Vapor Sensor TestingVAC Circuit Trace Safety Circuit Voltage Trace Safety Circuit Voltage TraceBlower Removal Remove the Blower to Gain Access to the Flue BaffleDip Tube Inspection and Replacement Remove the Blower to Gain Access to the Flue Baffle cont’dDip Tube Inspection Anode Inspection Anode Inspection and ReplacementInner Door Removal Inner Door Removal ProcedureInner Door Removal Procedure cont’d Inner Door Gasket ReplacementInner Door Gasket Replacement Procedure Inner Door Installation with Gasket Inner Door InstallationScreenLok Flame Arrestor Cleaning Procedure Arrestor CleaningCommon Terms Common TermsPart Name and Description Parts ListParts@bradfordwhite.com Techserv@bradfordwhite.com