Mitsubishi Electric EHST20C-VM6HA Service Manual page 45

Error code Title and display conditions
L3 Circulation water temperature overheat
protection
<DHW/Heating/LP/FS/OS>
Error code displayed when THW1 detects
a temp. ≥ 80ºC for 10 consecutive seconds
or THW2 detects a temp ≥ 80ºC for 10
consecutive seconds.
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
TH
THW1
THW
THW5B
Possible Cause
Insufficient system head
1
Reduced flow in primary water circuit
2
Due to 1 or more of the following;
Faulty pump, insufficient air purge, blocked-
strainer, leak in water circuit.
3 Valve operation fault
2-way valve (field supply) actuator fault
4
3-way valve actuator fault
5
Booster heater relay (BHC1, BHC2, BHCP)
6
operating fault
Power supply voltage increase
7
8 THW1 or THW3 or THW5B has become
detached from its holder.
9
THW1 or THW fault
0 FTC3 board failure
3-way valve actuator fault
1
Immersion heater relay (IHC) operating fault
2
3 THW5B fault
4
FTC3 board failure
Connector/terminal wire has become
1
detached or loose wiring.
2 Thermistor fault
3
FTC3 board failure
The thermistor on the wireless remote con-
4
troller or the main remote controller may be
defective. (when Room temp. is chosen for
the Heating operation and when Main Con-
troller or Room RC 1-8 is chosen for the
Room Sensor setting in the Initial setting)
Incorrect setting of the Dip switch(es)
5
Thermistor
Name
Room temperature thermisitor
Liquid temperature thermisitor
Flow water temperature thermisitor
Return water temperture thermisitor
Tank water temperture thermisitor
45
Diagnosis and action
1 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
2
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 rec-
ommended range.
Check valves on primary water circuit are
3
installed level.
4
Electrically test to determine fault.
1) Electrically test to determine fault.
5
2) Operate 3-way valve manually using the
main remote controller. (Refer to <Manual
operation> in 9.2).
3) Replace 3-way valve coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
Electrically test the relays (BHC1, BHC2,
6
BHCP) to determine fault.
See 10-6. for how to check.
Check the supply voltage.
7
8 Visually inspect location and reattach as
necessary.
Check resistance of thermistor against table
9
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
0 Replace board.
1) Electrically test to determine fault.
1
2) Operate 3-way valve manually using the
main remote controller. (Refer to <Manual
operation> in 9.2).
3) Replace 3-way valve coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
Check immersion heater relay (IHC)
2
Check resistance of thermistor against table
3
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
4
Replace board.
1 Visually check the terminals and connections
and reattachas appropriate.
Check resistance of thermistor against table
2
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
3
Replace board.
Replace wireless remote controller or main
4
remote controller
Check the Dip switch setting(s).
5
Open detection Short detection
-39ºC or below 88.5ºC or above
-39ºC or below 88.5ºC or above
-39ºC or below 88.5ºC or above
-39ºC or below 88.5ºC or above
-39ºC or below 88.5ºC or above