Bradford White UPV75 Series Service Manual page 9

UPV75 Series - Sequence of Operations
Power Up Sequence
1. Start Up: Upon power up, the control runs a safe-start check with a typical start-up delay of 5
seconds.
2. Simulative Resistive Device: To assure no outputs are energized if the "Simulated Resistive
Device" is out of range, the control will test the "Simulated Resistive Device" for proper operating
range. If the "Simulative Resistive Device" is out of range, the control LED immediately flashes 7
times with 3 second pause.
Normal Heating Sequence
1. Thermostat calls for heat: Prior to energizing blower, gas control checks safety circuit to ensure
the circuit is open. Normal switch positions in the safety circuit are as follows:
a. Pressure switch normally open.
b. Blower temperature switch normally closed.
If the safety circuit is closed, the control waits 4 seconds, gas control LED flashes 2 times with 3
second pause. Gas control waits 2 minutes then, blower runs for 30 seconds. This cycle repeats
until safety circuit opens.
2. Blower energizes.
3. Pressure switch proves blower/vent system operation: If the pressure switch does not close
within 30 seconds, the control LED flashes 3 times with 3 second pause. The blower runs for 30
seconds every 2 minutes trying to get the pressure switch or blower temperature switch to close.
This cycle repeats as long as there is a call for heat.
4. Blower pre-purge period (2 seconds).
5. Trial for pilot ignition (90 seconds).
a. The gas control lights the pilot by activating spark igniter and gas flow to pilot burner.
b. If flame is not sensed within 90 seconds, igniter and gas flow are deactivated, blower will
post purge and control LED flashes 6 times with 3 second pause.
6. Main burner ignition: After pilot flame is sensed, gas control activates main valve for main burner
ignition. The gas control will ignore flame and pressure switch signals for 3 seconds allowing for
main burner to stabilize.
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).
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