Bradford White TW4-75S-76B-3X - Manual (Page 11)

Steady state operation.
During Steady State Operation the Control Monitors:
Thermostat temperature sensor- When set point temperature is satisfied, gas valve is shut down and
blower will post purge for 15 seconds. Control LED flashes a short flash once every 4 seconds (idle) status
code.
Pressure switch / Blower temperature switch- If either switch opens, pilot valve and main valve is shut
down. The blower continues to runs for 30 seconds attempting to close the circuit. The control LED Flashes
3 times with 3 second pause.
Flame Sensor- If flame is lost, pilot & main valve are shut down, blower runs for 15 seconds. Control attempts
to re-light pilot 4 times. If unsuccessful, Blower is shut down and control proceeds to 5 minute lockout. Control
re-attempts to light pilot starting at normal heating sequence #2.
Thermostat satisfies.
Burner off.
Blower post purge (15 seconds).
9
8
10
7
Sequence of Operation
1. Simulated Resistive Device Fault:
a) If the resistance is greater than 70,000 Ohms - the gas control immediately turns off all outputs. Control waits
and monitors resistance for 30 seconds. If the resistance is greater than 70,000 ohms after 30 seconds, the
gas control proceeds to verify resistive delay for 2 minutes and flashes 8 times then once with a three second
pause. This process is repeated 5 times until the control either returns to normal operation or proceeds to flashing
7 times with a 3 second pause.
b) If the resistance is below 3000 ohms - The gas control immediately turns off all outputs and proceeds to flash
8 times then once with three second pause. The error self clears if the resistance returns to normal range for at
least 15 seconds.
2. Temperature Sensor Fault:
a) Temperature sensor detected open circuit - The gas control Immediately turns off all outputs and proceeds to
flash 8 times then twice with three second pause. The error self clears if the fault clears for at least 15 seconds.
b) Temperature sensors not reading the same temperature within ±5.5 °F - The gas control Immediately turns off
all outputs and proceeds to flash 8 times then twice with three second pause. The error self clears if the fault
clears for at least 15 seconds.
c) Water temperature in excess of TCO (Temperature Cut Off) limit - The gas control immediately turns off pilot &
main valve and proceeds to flash 4 times with 3 second pause. Blower continues to run until gas control is reset.
Power needs to be cycled to remove gas control from TCO lockout.
Page 11
pg11.pdf 1 pg11.pdf 1 3/24/06 4:57:44 PM 3/24/06 4:57:44 PM
Page 11