Bradford White URG2PV75H N Series Service Manual page 10

UPV75 Series
Normal Heating Sequence (cont.)
7. Steady state operation.
During steady state operation, the control monitors:
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 shut down. The blower continues to run 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 valves 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.
8. Thermostat satisfies. (Control LED flashing once every 4 seconds).
9. Burner off.
10. Blower post purges (15 seconds).
Abnormal 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 65,000 ohms after 30 seconds, the gas
control proceeds to verify resistive delay for 2 minutes and flashes 7 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 flammable vapor
lockout.
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 status 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, 3 times with 3
second pause. The status self clears if the fault clears for at least 15
seconds.
b. Temperature sensor not reading the same temperature within ±5.5°F –
The gas control immediately turns off all outputs and proceeds to flash 8
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Sequence of Operation