Bradford White UPDX2-75T6FRN - Manual (Page 9)

Sequence of Operation
1. Thermostat Calls for Heat.
Prior to energizing the blower, the gas control checks the safety circuit to insure 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 gas control waits 4 seconds, then the gas control LED flashes 2 times followed by
a 3 second pause. The gas control waits 2 minutes then, the blower runs for 30 seconds. This cycle repeats until
the safety circuit opens.
Power Up Sequence
1. Start Up.
Upon power up, the control runs a safe-start check with a typical start-up delay of 1-5 seconds.
2. Flammable Vapor Check.
To assure no outputs are energized if the “Flammable Vapor Sensor” is out of range, the control will test the
“Flammable Vapor Sensor” for proper operating range. If the “Flammable Vapor Sensor” is within range the
control resumes normal operation with no perceptible delay. If the “Flammable Vapor Sensor” is out of range, the
control LED immediately flashes 7 times followed by a 3 second pause.
Normal Heating Sequence
2. Blower Energizes.
4. Differential Pressure Switch Proves Blower/Vent System Operation.
a) If the pressure switch does not close within 30 seconds, the control LED Flashes 3 times followed by a 3 second
pause.
b) 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.
3. Blower Pre-purge Period (15 seconds).
5. Trial for Pilot Ignition (90 seconds).
a) The gas control lights the pilot by activating the spark igniter and gas flow to the pilot burner.
b) If flame is not sensed within 90 seconds, the igniter and gas flow are deactivated. The blower will post purge and
the gas control LED flashes 6 times followed by a 3 second pause.
6. Main Burner Ignition
After pilot flame is sensed, the gas control activates the main valve for main burner ignition. The gas control will
ignore flame and pressure switch signals for 3 seconds allowing for the main burner to stabilize.
Page 9
UPDX Series
9