Mitsubishi Electric EHSC-VM6A Service Manual page 38

Error code Title and display conditions
L4 Tank water temperature overheat protection
<DHW/Heating/LP/FS/OS>
Error code display when THW5B detects a
temp. ≥ 75ºC for 10 consecutive seconds.
L5 Indoor unit temperature thermistor
(TH1, TH2, THW1, THW2, THW5B) failure
<DHW/Heating/LP/FS/OS>
Error code displayed when thermistor is at
open or short (see table).
Exceptions
Error code will not be displayed for TH2;
During defrost and for 10 mins after defrost
operation.
Symbol
TH1
TH2
THW1
THW2
THW5B
L6 Circulation water freeze protection
<DHW/Heating/LP/FS/OS>
Error code displayed when THW1 detects
a temp. ≤ 1ºC for 10 consecutive seconds
or THW2 detects a temp. ≤ 3ºC for 10 con-
secutive seconds.
Exception
Error code will not be displayed if;
FS function is disabled,
Water circulation pump1 runs for 10 mins.
1 3-way valve actuator fault
2 Immersion heater relay (IHC) operating fault
3 THW5B fault
4
FTC3 board failure
1
Connector/terminal wire has become
detached or loose wiring.
2
Thermistor fault
3
FTC3 board failure
The thermistor on the wireless remote con-
troller or the main remote controller may be
defective.
4 Incorrect setting of the Dip switch(es)
Thermistor
Name
Room temperature thermisitor
Liquid temperature thermisitor
Flow water temperature thermisitor
Return water temperture thermisitor
Tank water temperture thermisitor
1 Insuffi cient system head
2 Reduced fl ow in primary water circuit. Due to
1 or more of the following;
Faulty pump, insuffi cient air purge, blocked-
strainer, leak in water circuit.
3
Valve operation fault
4
2-way valve (fi eld supply) actuator fault
5
3-way valve actuator fault
6
THW1 has become detached from its holder.
7
THW1 or THW2 fault
8 FTC3 board failure
Possible Cause
1
2
3
4
1
2
3
4
Open detection
-39.0ºC or below
-39.0ºC or below
-39.0ºC or below
-39.0ºC or below
-39.0ºC or below
1
2
3
4
5
6
7
8
38
Diagnosis and action
Electrically test to determine fault.
Check immersion heater relay (IHC)
See 10-6. for how to check.
Check resistance of thermistor against table
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
Replace board.
Visually check the terminals and connections
and reattachas appropriate.
Check resistance of thermistor against table
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
Replace board.
Check the Dip switch setting(s).
Short detection
88.5ºC or above
88.5ºC or above
88.5ºC or above
88.5ºC or above
88.5ºC or above
Refer to table in section 10-6. to determine if
system pump meets requirements.
If more head required either add an pump of
the same size or replace existing pump with
capacity model.
See 11. DISASSEMBLY PROCEDURE for
how to replace pump.
Check circulation pump (See 10-6. 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 flow amount is within the
recommended range.
Check valves on primary water circuit are in-
stalled level.
Electrically test to determine fault.
Electrically test to determine fault.
Visually inspect location and reattach as nec-
essary.
Check resistance of thermistor against table
in section 10-6.
Compare FTC3 detected temperature to hand
held detector.
Replace board.