Bradford White U-TW4-75S-76R-3N - Manual (Page 15)

Page 15
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.
Sequence of Operation
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