Service Manual

Sequence of Operation
Abnormal Operation (cont.)
3.Pressure Switch/Blower Temperature Fault:
a) PressureSwitchClosed at StartofCall for Heat - Thegas controlwaits4seconds then, proceeds to flash
2 times followed by a 3 second pause.Thegas controlwaits 2 minutes and then turns on theblower for 30
seconds. Theblower turns off after 30seconds and thegas controlwaits for th
e pressure switch to open. Any time
the pressure switch opens,theblower turns on (or stays on) and the control proceeds to waiting for the pressure
switch to close.
b) PressureSwitch or Blower TemperatureSwitch Failed Open - Thegas control runs theblo
wer for 30seconds
waiting for the pressure switch and/or blower temperature switch to close.If either switch does not closein30
seconds,theblower turns off and the control flashes 3 times followed by a 3 second pause.Thegas controlwaits
2 minutes before turning on theblower for anoth
er 30seconds to see the circuit close.This cycle repeats aslong
as there is acall for heat or until the circuit closes.
c) PressureSwitch or Blower TemperatureSwitch Opens DuringBurner Operation - Thegas control turns off
thepilot and main valve, runs theblower for 15seconds (inter-purge) waiting for the pressure switch and/or blower
temperature switch to close.If either switch fails to close, thegas control proceeds as described in 3b above.Ifthe
circuit closes again by the end of the inter-purge, the recyc
lecounter is incremented, if the recyclecount has
not reached itslimit (4), another trial for ignition begins. Ifthe recyclecount has been reached, the control
turns off theblower and flashes 6 times then 2 times followed by a 3 second pause.Thegas controlwaits5
minutes before repeating ignition sequence.
4. Trial For Ignition Fault:
a) PressureSwitch Opens DuringTrial - Thegas control turns off the igniter and pilot valve.Thegas control
proceeds as described in 3b above.Ifthe pressure switch closeswithin 30seconds,thegas controlwill continue
with trial for ignition starting at blower pre-purge.
b) Flame Not Sens
ed - Thegas control energizes the spark igniter attempting to lightthepilot and prove flame.If
flame is not sensed within 90seconds,the igniter turns off, thepilot valve is closed and thegas control runs the
blower through postpurge and flashes 6 times then once foll
owed by a 3 second pause.The controlwaits5
minutes before repeating the ignition sequence.
5. Flame Sensing Fault:
a) FlameLostDuring Run - Thegas control turns off thepilot and main valves and runs theblower for 15seconds
(inter-purge).Thegas control increments the recyclecount, if the recyclecount has not reached itslimit (4),
another trial for ignition begins. Ifthe recyclecount has been reached, thegas control t
urns off theblower and
flashes 6 times then 3 times followed by a 3 second pause.The controlwaits5minutes before repeating the
ignition sequence.
b) Flame Sensed Out of Sequence - thegas control only looks for pilot flame when theblower is running.Ifaflame
is present when thepilot valve is
not open the control proceeds to wait for flame loss and flashes 5 times followed
by a 3 second pause.This continuesuntil flame islost, once theflame signal islost, thegas control flashes 6
times then 4 times followed by a 3 second pause.Thegas controlwaits5minutes before repeating the ignition
sequence.
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UPDX Series
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