Mitsubishi Electric EHST20C-VM6HA Service Manual page 46

Error code Title and display conditions
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,
For 10 mins after water circulation pump1 is
switched on.
L7 3-way valve failure (Valve direction
defaults to DHW circuit)
<Heating/FS>
If a) and b) occur, L7 is displayed;
a) No change on THW1 (under 1 °C for 20
minutes from unit starts operation)
b) THW5B goes up in Heating (or FS)
mode. (over 1 °C for 20 minutes)
Exception
If simultaneous Heating and DHW operation
is selected error code will not be displayed.
L8 Heating operation error
<Heating/FS>
If a), b) and c) occur, L8 is displayed;
a) No change on THW1 and THW5B
(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 - THW < -5 °C
(for 10 minutes continuously)
Possible Cause
Insufficient system head
1
Reduced flow in primary water circuit. Due to
2
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
6 THW1 has become detached from its holder.
7 THW1 or THW fault
8
FTC3 board failure
3-way valve actuator fault
1
2 THW1 or THW5B fault
3
FTC3 board failure
The thermistor on the wireless remote con-
troller or the main remote controller may be
defective.
Incorrect setting of the Dip switch(es)
4
5 THW1 or THW5B has been detached from
its holder.
1
THW1 has become detached from its
holder.
2 Booster heater fault
3 THW1 or THW or THW5B fault
4 FTC3 board failure
46
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
recommended range.
Check valves on primary water circuit are in-
3
stalled 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."
6 Visually inspect location and reattach as
necessary.
Check resistance of thermistor against table
7
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
8
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 resistance of thermistor against table
2
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
3
Replace board.
Check the Dip switch setting(s)
4
5 Visually inspect location and reattach as
necessary.
1
Visually inspect location and reattach as
necessary.
2 Electrically test to determine fault.
See 10-6. for how to check.
Check resistance of thermistor against table
3
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
4 Replace board.