28
controls and swItches
Thismodelisprovidedwiththreepressureswitches.Theseswitches
areessentialtothesafeandproperoperationoftheunit.Allswitches
arewiredinseries. Thecontrollerisset uptoshutthe unitdown
wheneverthereisafailureofanyoftheswitches.Itisimportantto
understandthepurposeofeachswitch.
FIGURE 12.

Blower prover swItch

(SEEFIGURE12)
TheBlowerProverSwitch isprovidedontheheater toverifythat
thefanisoperating.Itisapositivepressureswitchwhoseelectrical
contactsarenormallyopen.Whenthefan increasesthepressure
intheburner,thepressureswitchwillallow theelectricalcontacts
toclose.Thepressureswitchis connectedtotheburnertap bya
pieceoftygontubing.This tubingmustbeconnected inorderfor
theswitchtochangetheelectricalcontacts.Thecontrollerrequires
thattheelectricalcontactsonthisairowswitchbeopenbeforeit
willallowtheblowertocomeon.

BlocKed eXhaust swItch

(SEEFIGURE12)
TheBlockedExhaustSwitchis setuptoshut theunitoffwhen a
build-upofpositivepressureintheexhaustventpipe occurs.This
switchisa p ositive pressure switch that requires an increase in
pressuretochangetheelectricalcontactsfromnormallyclosedto
open.Whenthisswitchpreventstheunitfromigniting,mostlikelythe
exhaustisblockedbysomemeans.Checktoseeifthecondensate
isallowedtoowfreelyfromtheexhaustelbowandforobstructions
intheexhaustventing andexhaustventterminal.Also verifythat
theventlengthdoesnotexceedthemaximumallowedasshownin
theVentSectionofthismanual.

BlocKed IntaKe swItch

(SEEFIGURE12)
TheBlockedIntakeSwitchissetuptoshuttheunitoffwhena
build-upofnegativepressureintheintakeairpipeoccurs.This
switchisanegativepressureswitchthatrequiresanincreasein
negativepressuretochangetheelectricalcontactsfromnormally
closedtoopen.Theswitchisconnectedtothepressuretaponthe
PVCpipeconnectedtotheinletoftheblower.Whenthisswitch
preventstheunitfromigniting,mostlikelytheintakeisblocked.
Verifythatthescreenontheintakeairconnection(conventional
vent),theintakeairpipeandtermination(directventinstallations)
arefreeofobstructionsthatmaypreventairfromenteringtheunit.
Insurethescreenonintakeairconnectionhasbeenremovedon
directventinstallations,seeFigure 18B.Alsoverifytheintake
airpipelengthdoesnotexceedthemaximumallowedasshown
intheVentSectionofthismanual.

on/off swItch

TheON/OFFSwitchisasingle-pole,single-throwrockerswitch.This
switchprovides120Vfromthelinesourcetotheheater.

cautIon

the water he ater I s po larItY sensIt Ive. Before
applYInG electrIcItY to thIs heater Be certaIn that
supplY neutral wIre to Ground checK IndIcates
ZERO VOLTAGE.

hot surface IGnIter

TheHotSurfaceIgniterisadevicethatignitesthemainburnerby
hightemperature(>1800°For >982°C).When120VACisapplied
totheigniter,sufcientheatisgeneratedtoignitethemainburner.
Althoughimprovementshavebeenmadetostrengthentheigniter,
itisstillfragileandcaremustbetakenwhenhandlingtheigniterto
preventbreakage.