A.O. Smith Boiler VB/VW- 750 User Manual

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40
UIM OPERATING PROCEDURES
FIGURE 20. UIM, USER INTERFACE MODULE
The UIM receives commands from the user and displays operational
informationtotheuserviaanLCD(liquidcrystaldisplay)uptoeleven
LED’s,andvetouchswitches.TheLCDprovidesinformationto
the user by the use of 10 menu-activated screens. Within each of
the screens, helpful information can be displayed by pressing the
“Help”button.TheLED’svisuallyinformtheuseraboutthemode
the system is in. The touch switches allow the user to control the
operation of the system. The operation of these parts is described
in the following section:
UIM Screens:
On all screens a double vertical bar appears on the right side of
the display each time a key is touched to indicate that a key has
beenactivated.Onseveralscreensanindicator“>”appearson
the left side of the display to indicate the active line. The “Up/
Down”keysareusedtomovetheindicatortothedesiredlineand
the“Select”keyispressedtoselecttheline.Also,onmostofthe
screens, up/down arrows appear on the right side of the screen
to indicate that there is additional lines either above or below the
displayed four lines.
• Menu Screen:
Displayedwhentheuserpressesthe“Menu”key.Thisscreen
is the selection point for the other 9 screens.
• Temperature Screen:
Displays the sensed temperatures of the Outlet, Inlet, and
Tankprobes.AlsodisplayedisthecalculatedDeltaT(Outlet
minusInlet)forthesystem.Shorted(“Short”)anddisconnected
(“----”)probesarealsodisplayed.
• System Status Screen:
This screen is used to view the status of switch inputs and output
states.Anasterisk(*)isdisplayednexttothelabelwhenthe
statusis“True”(thedescriptionisfullled).Forexample,if
waterisowing,ordetectedbytheowsensor,thenan“*”will
appearinfrontoftheFlowlabel(i.e.*Flow).Anotherexample
would be the ECO switch. If the outlet temperature is too high
the display will show: *ECO.
The System monitors the inputs of these times:
• MRHL,BlockedInlet,BlockedFlue,LowGas,HiLimit,andHi
Gas - at all times for a fault condition.
• Tstat-atalltimesforopen/closedconditions.
• Flow-foranonconditionwhenthepumpison(nocheckforoff
state)
• BlowerProver-whentheBlowerison.
• IgniterCurrent-foranonconditionapproximately18seconds
after the Igniter is turned on until the igniter is turned off and an
off condition at all other times.
• Flame-foranonconditionapproximately5secondsafterthe
gas valve is turned on until the valve is turned off and at all other
times for an off condition.
Control Status Screen:
Displays the status that the MCB micros are in. The MCB has
5 possible states and the FCB have 9. The normal MCB states
sequence is to move from Idle to Pre-Circulate when a call for
heatisinitiated.OnceheathasbeensatisedortheThermostat
is opened, the sequence moves to Post-Circulate and then back to
Idle. If a fault occurs at any time, the process jumps out of sequence
and goes directly to the appropriate Hard or Soft Fault state.
Description of MCB control states:
• Idle:
Theyellow“Standby”LEDisturnedonandthesystemwaits
foraheatrequest(determinedbytheThermostatorcontrolling
probeinputs).Alloutputsareoffinthisstateexceptthatifthe
Post-Circulate time is set to continuous, the pump will be on.
When the heat request is received, the system moves to the
Pre-Circulate state.
• Pre-Circulate:
TheyellowLEDisturnedoffandthegreen“Running”LEDis
turned on. The green LED will remain on for all other states
except the fault states. Cold purging clears out any combustion
gas that may be in the combustion chamber. When purging is
complete the system moves to the Heat State.
• HeatStage
The system will command the FCB micros to start their heat
sequence. will be activated in order based on an algorithm that
determines how much heat is needed. The system will remain in
thisstateuntiltheheatrequestissatised,theTstatisopened,
or a fault occurs.
• SoftFaultState:(See“FaultDescription”sectionforlistofsoft
andAutoResetfaults.)
The pump remains on for the selected post-circulate time to
cycle the hot water out of the boiler. The FCB is commanded
to shut down and the Alarm output is turned on. The green LED
turnsoffandthered“Service”turnson.TheMCBremainsin
this state until one of the following occurs:
• Onehourpasses(automaticrestartafteronehour)
• IfCommunicationserrorsystemwillautomatically
restart if communications re-establishes.
• IfuserpressesSelectkeywhilecurrenterrorscreenis
displayed(Hardreset).
• Ifhigh-limiterror-theoutlettemperaturedropsbelowthe
highlimittrippointminusthehighlimitdifferential.(outlet
watertemperaturedropstosafelevel).Thefaultislogged
in the error history when the fault state is exited.
• HardFaultState:(See“FaultDescription”sectionforlistof
softandAutoResetfaults.)Thepumpremainsonforthe
selected post-circulate time to cycle the hot water out of the
boiler. The FCB is commanded to shut down and the Alarm
output is turned on. The green LED turns off and the red
“Service”turnsonandoff(ashes).Theonlywaytoexit
this state is for the user to press the Select key while the
current error screen is displayed. The fault is logged in the
error history when the fault state is exited.
While the MCB is in the Heating mode the FCB moves from Idle, to
Pre-Purge, to Heat Igniter, to Check for Flame, and then to Heating.

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