Bradford-White Corp U4TW50TFRN, U4TW40TFRN, U4TW60TFRN service manual* Sequence of Operation

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Sequence of Operation

Abnormal Operation (cont’d)

B)Pressure switch or blower temperature switch failed to close: The gas control runs the blower for 30 seconds waiting for the pressure switch and/or the blower temperature switch to close. If either switch does not close in 30 seconds, the blower turns off and the control flashes 3 times with a 3 second pause. The gas control waits 2 minutes before turning on the blower for another 30 seconds to see the circuit close. This cycle repeats as long as there is a call for heat or until the circuit closes.

C)Pressure switch or blower temperature switch opens during operation: The gas control turns off the pilot and main valve, runs the blower for 15 seconds (inter-purge) waiting for the pressure switch and/or the blower temperature switch to close. If either switch fails to close, the gas control proceeds as described in 3b above. If the circuit closes again by the end of the inter-purge, the recycle counter is incre- mented, if the recycle count has not reached its limit (4), another trial for ignition begins. If the recycle count has been reached, the gas control turns off the blower and flashes 6 times, then 2 times with a 3 second pause. The gas control waits 5 minutes before repeating ig- nition sequence.

4.Trial for Ignition Fault:

A)Pressure switch opens during trial: The gas control turns off the ig- niter and pilot valve. The gas control proceeds as described in 3b above. If the pressure switch closes within 30 seconds the gas control will continue with a trial for ignition starting at blower pre-purge.

B)Flame Not Sensed: The gas control energizes the spark igniter at- tempting to light the pilot and prove flame. If flame is not sensed within 90 seconds, the spark igniter turns off, the pilot valve is closed. The gas control LED flashes 6 times then 1 time with 3 sec- ond pause. The control waits 5 minutes before repeating the ignition sequence.

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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 DiagramPower Up Sequence Sequence of OperationNormal 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 Maintenance Burner Cleaning ProcedureBurner 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 Replacement Blower InstallationBlower Removal Blower Temperature Switch Testing Blower Installation cont’dBlower Temperature Switch Testing Switch Setting Blower Temperature Switch Testing cont’dBlower Temperature Switch Replacement Blower Temperature Switch ReplacementThermal Well Testing Thermal Well TestingDetermine Tank Temperature Thermal Well Testing cont’dDetermine Water Temperature Inside Tank Component Disassembly Sensor Resistance at Various TemperaturesGas Control & Thermal Well Removal From Water Heater Gas Control Removal Gas Control Assembly Gas Control Assembly to the Thermal WellGas 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 BaffleRemove the Blower to Gain Access to the Flue Baffle cont’d Dip Tube Inspection and ReplacementDip Tube Inspection Anode Inspection Anode Inspection and ReplacementInner Door Removal Inner Door Removal ProcedureInner Door Gasket Replacement Inner Door Removal Procedure cont’dInner 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