Mitsubishi EHST20C-VM2C - Page 73

73
No. Fault symptom Possible cause Explanation - Solution
22
Waterdischargesfrom
expansionreliefvalve
- part of Inlet Control
Group
(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–expansionrelief valve may be
damaged.
2. Turnthehandleontheexpansionreliefvalvetocheckforforeignobjects
inside.Iftheproblemisnotstillsolved,replacetheexpansion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precharge.
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ow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.
23
Noisywatercirculation
pump
Airinwatercirculationpump. Use manual and automatic air vents to remove air from system.
Topupwaterifnecessarytoachieve1baronprimarycircuit.
24 Noiseduringhotwater
drawofftypically
worseinthemorning.
1. Looseairingcupboardpipework. 1. Installextrapipefasteningclips.
2. Heatersswitchingon/off. 2. Normal operation no action necessary.
25 Mechanical noise
heardcomingfromthe
cylinder unit.
1. Heatersswitchingon/off. Normal operation no action necessary.
2. 3-wayvalvechangingposition between
DHWandheatingmode.
26
Water circulation pump
runs for a short time
unexpectedly.
Watercirculationpumpjampreventionmechanism
(routine) to inhibit the build-up of scale.
Normal operation no action necessary.
27 Milky/Cloudywater
(Sanitary circuit)
Oxygenatedwater Waterfromanypressurisedsystemwillreleaseoxygenbubbleswhenwateris
running.Thebubbleswillsettleout.
28 Heatingmodehas
been on standby for
alongtime(does
not start operation
smoothly.)
Thetimeof“Delay”setin“Economysettings
for pump” is too short. (Go to “Service menu”
→“Auxiliarysettings”→“Economysettingsfor
pump”).
Increasethetimeof“Delay”in“Economysettingsforpump”.
29 The cylinder unit
thatwasrunningin
theheatingmode
beforepowerfailure
isrunningintheDHW
modeafterpower
recovery.
Thecylinderunitisdesignedtoruninanoperation
modewithahigherpriority(i.e.DHWmodeinthis
case)atpowerrecovery.
•Normaloperation.
•AftertheDHWmax.operationtimehaselapsedortheDHWmax.temperature
hasbeenreached,theDHWmodeswitchestotheothermode(ex.Heating
mode).
30
CoolingmodeisNOT
available.
DIP SW2-4 is OFF. TurnDIPSW2-4toON.(Referto“6-19.DIPswitchfunctions”.)
31
Thecoolingsystem
doesnotcooldownto
the set temperature.
1. Whenthewaterinthecirculationcircuitisun-
dulyhot,Coolingmodestartswithadelayfor
the protection of the outdoor unit.
1. Normal operation.
2. When the outdoor ambient temperature is
lowerthan the presettemperaturethatacti-
vatesthe freeze statfunction,Coolingmode
doesnotstartrunning.
2. TorunCoolingmodeoverridingthefreezestatfunction,adjustthepreset
temperaturethatactivatesthefreezestatfunction.
(Referto"<Freezestatfunction>"onPage49.)
32
The electric heaters are
activated shortly after
DHW or LP mode starts
runningafterCooling
mode.
ThesettingtimeperiodofHeat-pump-onlyopera-
tion is short.
AdjustthesettingtimeperiodofHeat-pumponlyoperation.(Referto“<Electric
heater(DHW)>onPage47.
33
DuringDHWorLP
modefollowingthe
coolingmode,error
L6(circulationwater
freezeprotectionerror)
occurs and the system
stops all the operations.
TheunitrunsinCoolingmodewhentheoutdoor
ambienttemperatureislowerthan10ºC(outside
oftheguaranteedoperatingrange).
(Whendefrostingoperationisrunningatsucha
lowoutdoorambienttemperatureafterCooling
modeisswitchedtoDHWorLPmode,thewater
temperatureinthecoolingcircuitdropstoolow,
whichcouldresultinL6errortostopalltheopera-
tions.
Donot runCoolingoperationwhenthe outdoorambienttemperatureis lower
than10ºC.
ToautomaticallystoporrecoveronlyCoolingoperationandkeepotheropera-
tionsrunning,thefreezestatfunctioncanbeused.Setthepresettemperature
thatactivatesthefreeze stat function to adjust the outdoor ambient tempera-
tureasfollows.(Referto"<Freezestatfunction>"onPage49.)
Outdoor ambient temperature Cooling operation
3ºChigherthanthepresettemperature Stop
5ºChigherthanthepresettemperature Recover
OCH570C