Mitsubishi Electric EHST20C-VM6HB Service Manual page 56

Error code Title and display conditions
L8 Heating operation error
* "" is displayed in "Request code: 567" in "Run-
ning information".
<Heating/FS>
If a), b) and c) occur, L8 is displayed;
a) No change on THW1 and THW5
(under 1 °C for 0 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)
Heating operation error
* "a" is displayed in "Request code: 567" in
"Running information".
Heating operation error
* "c" is displayed in "Request code: 569" in
"Running information".
Low primary circuit (Heat source side) flow
L9
rate detected by flow switch
* "1" is displayed in "Request code: 569" in "Run-
ning information".
<DHW/Heating/LP/FS>
Error code displayed when flow switch detects
low flow rate for 10 seconds.
Exception
For 1 min after water circulation pump1 is
switched on.
Low primary circuit (Zone1 side) flow rate
detected by flow switch
* "" is displayed in "Request code: 569" in "Run-
ning information".
OCH531
Possible Cause
1. THW1 has become detached from its
holder.
. Booster heater fault
. THW1 or THW or THW5 fault
FTC4 board failure
4.
1. THW6 has become detached from its
holder.
. THW6 or THW7 fault
FTC4 board failure
.
1. THW8 has become detached from its
holder.
. THW8 or THW9 fault
FTC4 board failure
.
Insufficient system head
1.
Reduced flow in primary water circuit
.
Due to 1 or more of the following;
Faulty pump, insufficient air purge,
blocked strainer, leak in water circuit.
. Valve operation fault
2-way valve (field supply) actuator fault
4.
Connector/terminal wire has become
5.
detached or loose wiring.
Flow switch fault
6.
Incorrect setting of the SW2-2
7.
FTC4 board failure
8.
Insufficient system head
1.
Reduced flow in primary water circuit
.
Due to 1 or more of the following;
Faulty pump, insufficient air purge,
blocked strainer, leak in water circuit.
Terminal wire has become detached
.
or loose wiring.
Flow switch fault
4.
Incorrect setting of the SW3-2
5.
FTC4 board failure
6.
56
Diagnosis and action
1. Visually inspect location and reattach as
necessary.
. Electrically test to determine fault.
See 10-6. for how to check.
Check resistance of thermistor against ta-
.
ble in section 10-6.
Compare FTC4 detected temperature to
hand held detector.
4. Replace board.
1. Visually inspect location and reattach as
necessary.
Check resistance of thermistor against ta-
.
ble in section 10-6.
Compare FTC4 detected temperature to
hand held detector.
. Replace board.
1. Visually inspect location and reattach as
necessary.
Check resistance of thermistor against ta-
.
ble in section 10-6.
Compare FTC4 detected temperature to
hand held detector.
. Replace board.
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
.
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
.
installed level.
4. Electrically test to determine fault.
Visually check the CN2F connector and
5.
IN terminal and reattach if necessary.
6. Electrically test to determine fault.
See 10-6. for how to check.
7. Check the SW2-2 setting.
8. Replace board.
1. If more head required either add an pump
of the same size or replace existing 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.
. Visually check the IN terminal and reat-
tach if necessary.
4. Electrically test to determine fault.
Check the SW3-2 setting.
5.
6. Replace board.