Specifications

64
XII Operation
1) TheFCMboilerusesamicroprocessorbasedcontrol,knownasa“MCBA”,tomanageallboilerfunctions 
includingamesupervisionandmodulation.Twosetpointor“target”boilersupplytemperaturesarestoredinthe
MCBA’smemory;oneforspaceheatingandonefordomesticwaterproduction.Ifanoutdoortemperaturesensor
isconnectedtotheboiler,thespaceheatingsupplysetpointwillautomaticallyadjustdownwardsastheoutdoor
temperatureincreases.Formoreinformationonthisfeatureseethediscussiononboilerwaterresetbelow.
 TheMCBAmodulatestheboilerinputbyvaryingthefanspeed.Asthefanspeedincreases,sodoesthe 
amountofgasdrawnintotheblower.Asaresult,afairlyconstantair-fuelratioismaintainedacrossallinputs. 
 TheMCBAdeterminestheinputneededbylookingatbothcurrentandrecentdifferencesbetweenthesupply 
temperatureandthesetpointtemperature.Asthesupplytemperatureapproachesthesetpointtemperature,thefanwill
slowdownandtheinputdrop.Dependingonthemodelboiler,theminimuminputisbetween¼and1/5ofmaximum
input.
 TheMCBAalsomonitorsboilerreturnanduetemperatures.Inaddition,allothersafetycontrols,includingthelow
watercut-offandsafetylimit,areconnectedintotheMCBA.TheMCBAusesinputfromallofthesecontrolstoeither
shutdowntheboilerwhenanunsafeconditionexistsor,insomecases,tocorrecttheproblem.
2) Thedisplaypanelhasthreeprimarymodesofoperation.Theseare:
• StandbyMode–Displaysboiler’scurrentstatus.Thisisthedefaultoperatingmode.
• ParameterMode–Usedtochangecontrolsettings
• InformationMode–Displaysboileroperatingtemperatures
 Undernormalconditions,theboilerisinstandbymodeandthedisplaylookslikethatshowninFigure12.1.Thethree
digitstotherightofthedecimalpointaretheboiler’ssupplytemperature.Thedigittotheleftofthedecimalpointisthe
boiler’sstatuscode.Alistofstatuscodes,andtheirmeanings,isshowninTable12.3.
 Figure12.2isamapofthemenustructureforthecontrolpanel.Pushthemodekeytomovefromonemodetothenext.
Asyouchangemodes,themodeyouareenteringisshownonthedisplay:
a) “PArA”
forParameterMode
b) “Info”forInformationMode
c) “Stby”forStandbyMode.Uponenteringstandbymode,“Stby”willbrieyappearonthedisplayandthenthe
display willshowtheboiler’sstatusalongwiththesupplytemperature(Figure12.1).
Thecontrolwillreturntostandbymodefromanyothermodeifnokeyispressedfor20minutes.
Figure 12.1: Normal Display In Standby Mode