Mitsubishi EHST20C-VM2C - Page 72

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No. Fault symptom Possible cause Explanation - Solution
14 In2-zonetempera-
ture control, only
Zone2 does not
reach the set tem-
perature.
1. WhenZone1andZone2arebothinheating
mode,thehot water temperatureinZone2
doesnotexceedthatinZone1.
1. Normal action no action necessary.
2. Faultywiringofmotorizedmixingvalve 2. Refertoinstallationmanual,"5.3Wiringfor2-zonetemperaturecontrol".
3. Faultyinstallationofmotorizedmixingvalve 3. Checkforcorrectinstallation.(Refertothemanualincludedwitheachmotor-
izedmixingvalve.)
4. IncorrectsettingofRunningtime 4. CheckforcorrectsettingofRunningtime.
5. Motorizedmixingvalvefailure 5. Inspectthemixingvalve.(Refertothemanualincludedwitheachmotorized
mixingvalve.)
15
When a PUHZ-FRP
outdoor unit is con-
nected, DHW or Heat-
ingoperationcannot
run.
The outdoor unit is set to have operation of the
indoor unit of air conditioner take precedence over
that of the cylinder unit, and in the main remote
controllersettings"Electricheater(Heating)"or
"Electricheater(DHW)"isturnedoff.
TurnONElectricheater(Heating)or Electric heater(DHW)usingthemainre-
mote controller.
16 When a PUHZ-FRP
outdoor unit is con-
nected and is in heat
recovery operation,
the set temperature
is not reached.
Whentheoutdoorunitissettohavecooling
operation of the indoor unit of air conditioner take
precedence over that of the cylinder unit, the out-
door unit controls the frequency of the compres-
soraccordingtotheloadofairconditioner.The
DHWandheatingrunaccordingtothatfrequency.
Normal operation no action necessary.
IfAir-to-Watersystemisgiven priority in operation, compHzcanberegulated
dependingontheloadofDHWorHeating.Formoredetails,refertothePUHZ-
FRP installation manual.
17 After DHW operation
room temperature
risesslightly.
AttheendoftheDHWmodeoperationthe3-way
valvedivertshotwaterawayfromtheDHWcircuit
intospaceheatingcircuit.
This is done to prevent the cylinder unit compo-
nentsfromoverheating.
Theamountof hot water directed into thespace
heatingcircuit variesaccordingtothetype ofthe
systemandofthepiperunbetweentheplateheat
exchangerandthecylinderunit.
Normal operation no action necessary.
18
The room tempera-
turerisesduringDHW
operation.
3-wayvalvefailure Checkthe3-wayvalve.
(i)Manuallyoverride3-wayvalveusingthemainremotecontroller.(Referto
<Manualoperation>in "9-4. Service menu".)Ifthe3-wayvalvedoesnot
function,goto(ii)below.
(ii)Replace3-wayvalvecoil.Ifthe3-wayvalvecoilisreplacedbutthe3-way
valvedoesnotfunctiongoto(iii)below.
(iii)Replace3-wayvalve.(Referto"11.DISASSEMBLYPROCEDURE".)
19 Waterdischarges
from pressure relief
valve.
(Primary circuit)
1. If continual – pressure relief valve could bite
foreignobjectsandthevalveseatmaybe
damaged.
1. Turnthehandleonthepressurereliefvalveseveralturns.Ifleakagepersists,
replacethepressurereliefvalvewithanewone.
2. Ifintermittent–expansionvesselchargemay
have reduced/bladder perished.
2. Checkpressureinexpansionvessel.
Rechargeto1barifnecessary.
Ifbladderperishedreplaceexpansionvesselwithanewone.
20 Waterdischarges
from pressure relief
valve.
(Sanitary circuit)
1. Ifcontinual–eldsuppliedpressurereducing
valvenotworking.
1.
Checkfunctionofpressurereducingvalveandreplaceifnecessary.
2. If continual – pressure relief valve could bite
foreignobjectsandthevalveseatmaybe
damaged.
2. Turnthehandleonthepressurereliefvalveseveralturns.Ifleakagepersists,
replacethepressurereliefvalvewithanewone.
3. Ifintermittent–expansionvesselchargemay
have reduced/bladder perished.
3. Checkgas-sidepressureinexpansionvessel.
Rechargetocorrectprechargepressureifnecessary.
Ifbladderperishedreplaceexpansionvesselwithanewonewithappropriate
pre-charge.
4. DHWtankmayhavesubjectedtobackow. 4. Check the pressure in DHW tank. If pressure in DHW tank is similar to that in
theincomingmains,coldwatersupplythatmergeswithincomingmainswa-
tersupplycouldowbacktoDHWtank.Investigatesourceofback-feedand
rectifyerrorinpipework/ttingconguration.Adjustpressureincoldsupply.
21 Waterdischarges
from temperature
and pressure relief
valve
(EH*T20*-MHCW only)
(Sanitary circuit)
1. Ifcontinual–eldsuppliedpressurereducing
valvenotworking.
1. Checkfunctionofpressurereducingvalveandreplaceifnecessary.
2. If continual – temperature and pressure relief
valvecouldbiteforeignobjectsandthevalve
seatmaybedamaged.
2. Turn the handle on the temperature and pressure relief valve several turns.
Ifleakagepersists, replace thetemperatureandpressurereliefvalvewitha
newone.
3. Ifintermittent–expansionvesselchargemay
have reduced/bladder perished.
3. Checkgas-sidepressureinexpansionvessel.
Rechargetocorrectprechargepressureifnecessary.
Ifbladderperishedreplaceexpansionvesselwithanewonewithappropriate
pre-charge.
4. DHWtankmayhavesubjectedtobackow. 4. Check pressure in DHW tank. If pressure in DHW tank is similar to that in the
incomingmains,coldwatersupplythatmerges with incoming mains water
supplycouldflowbacktoDHW tank. Investigate source of back-feed and
rectifyerrorinpipework/ttingconguration.Adjustpressureincoldsupply.
5. Unit has overheated – thermal controls have
failed.
5. Switchoffpowertotheheatpumpandimmersionheaters.
Leavewaterrunning.
Waituntildischargestops.Isolatewatersupplyandreplaceiffaulty.
OCH570C