Mitsubishi EHST20C-VM2C - Heating Operation Error; Low Primary Circuit Flow Rate Detected by Flow Sensor

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Error code Title and display conditions Possible Cause Diagnosis and action
L8 Heating operation error
Note: “3” is displayed in “Request code: 567” in
“Runninginformation”.
<Heating/FS>
If a), b) and c) occur, L8 is displayed;
a) NochangeonTHW1andTHW5
(under1°Cfor20minutesfromunitstarts
operation)
b) NochangeonTHW1
(under1°Cfor10minutesfromboosterheater
starts operation)
c) THW1−THW2<−5°C
(for 10 minutes continuously)
1. THW1 has become detached from its
holder.
1. Visually inspect location and reattach as
necessary.
2. Booster heater fault 2. Electrically test to determine fault.
See"10-6.CheckingComponentParts'
Function"forhowtocheck.
3. THW1 or THW2 or THW5 fault 3. Checkresistanceofthermistoragainst
tablein"10-6.CheckingComponentParts'
Function".
Compare FTC detected temperature to
hand held detector.
4. FTC board failure 4. Replace board.
Heating operation error
Note:
“A” is displayed in “Request code: 567” in
“Runninginformation”.
1. THW6 has become detached from its
holder.
1. Visually inspect location and reattach as
necessary.
2. THW6 or THW7 fault 2. Checkresistanceofthermistoragainst
tablein"10-6.CheckingComponentParts'
Function".
Compare FTC detected temperature to
hand held detector.
3. FTC board failure 3. Replace board.
Heating operation error
Note: “C” is displayed in “Request code: 567” in
“Runninginformation”.
1. THW8 has become detached from its
holder.
1. Visually inspect location and reattach as
necessary.
2. THW8 or THW9 fault 2. Checkresistanceofthermistoragainst
tablein"10-6.CheckingComponentParts'
Function"
Compare FTC detected temperature to
hand held detector.
3. FTC board failure 3. Replace board.
L9
Lowprimarycircuit(Heatsourceside)ow
ratedetectedbyowsensor
Note: “1” is displayed in “Request code: 569” in
“Runninginformation”.
<DHW/Heating/LP/FS>
Errorcodedisplayedwhenowsensordetects
lowowratefor10seconds.
Exception
For1minuteafterwatercirculationpump1is
switchedon.
1. Insufcientsystemhead 1. Refertotablein"10-6.CheckingCom-
ponentParts'Function"todetermineif
system pump meets requirements.
If more head required either add a pump
ofthesamesizeorreplaceexistingpump
withcapacitymodel.
See"11.DISASSEMBLYPROCEDURE"
forhowtoreplacepump.
2. Reducedowinprimarywatercircuit
Dueto1ormoreofthefollowing;
Faultypump,insufcientairpurge,
blockedstrainer,leakinwatercircuit.
2. Checkcirculationpump(See"10-6.Check-
ingComponentParts'Function"forhowto
check).
Openpurgevalvetoremovetrappedair.
Checkthestrainerforblockages.
Checktheprimarywatercircuitforleaks.
Checkthattheowamountiswithinthe
recommendedrange.
3. Valve operation fault 3. Checkvalvesonprimarywatercircuitare
installed level.
4.
2-wayvalve(localsupply)actuator
fault
4. Electrically test to determine fault.
5. Connector/terminalwirehasbecome
detachedorloosewiring.
5. Visually check the CN1A connector and
IN2 terminal and reattach if necessary.
6. Flowsensorfault 6. Electrically test to determine fault.
See"10-6.CheckingComponentParts'
Function"forhowtocheck.
7. IncorrectsettingoftheSW2-2 7. ChecktheSW2-2setting.
8. FTC board failure 8. Replace board.
Lowprimarycircuit(Zone1side)owrate
detectedbyowswitch
Note: “2” is displayed in “Request code: 569” in
“Runninginformation”.
1. Insufcientsystemhead 1. If more head required either add a pump of
thesamesizeorreplaceexistingpump.
2. Reducedowinprimarywatercircuit
Dueto1ormoreofthefollowing;
Faultypump,insufcientairpurge,
blockedstrainer,leakinwatercircuit.
2. Checkcirculationpump(See"10-6.Check-
ingComponentParts'Function"forhowto
check).
Openpurgevalvetoremovetrappedair.
Checkthestrainerforblockages.
Checktheprimarywatercircuitforleaks.
Checkthattheowamountiswithinthe
recommendedrange.
3. Terminalwirehasbecomedetached
orloosewiring.
3. Visually check the IN3 terminal and reat-
tach if necessary.
4. Flowswitchfault 4. Electrically test to determine fault.
5. IncorrectsettingoftheSW3-2 5. ChecktheSW3-2setting.
6. FTC board failure 6. Replace board.
OCH570C