Mitsubishi Electric EHSD-MED Service Manual page 46

Check code Title and display conditions
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 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−THW2 < −5°C
(for 10 minutes continuously)
Heating operation error
Note: "A" is displayed in "Request code: 567" in
"Running information".
Heating operation error
Note: "C" is displayed in "Request code: 567" in
"Running information".
L9 Low primary circuit (Heat source side) flow
rate detected by flow sensor
Note: "1" is displayed in "Request code: 569" in
"Running information".
<DHW/Heating/Cooling/LP/FS>
Check code displayed when flow sensor detects
low flow rate for 10 seconds.
Exception
For 1 minute after water circulation pump1 is
switched on.
Low primary circuit (Zone1 side) flow rate
detected by flow switch
Note: "2" is displayed in "Request code: 569" in
"Running information".
OCH712C
Possible Cause
1. THW1 has become detached from its
holder.
2. Booster heater fault
3. THW1 or THW2 or THW5B fault
4. FTC board failure
1. THW6 has become detached from its
holder.
2. THW6 or THW7 fault
3. FTC board failure
1. THW8 has become detached from its
holder.
2. THW8 or THW9 fault
3. FTC board failure
1. Insufficient system head
2. 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
3. Valve operation fault
4. 2-way valve (local supply) actuator fault 4.
5. Connector wire has become detached
or loose wiring.
6. Flow sensor fault
7. Incorrect setting of the SW2-2
8. FTC board failure
1. Insufficient system head
2. 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
3. Terminal wire has become detached
or loose wiring.
4. Flow switch fault
5. Incorrect setting of the SW3-2
6. FTC board failure
46
Diagnosis and action
1. Visually inspect location and reattach as
necessary.
2. Electrically test to determine fault.
See "10-6. Checking Component Parts'
Function" for how to check.
3. Check resistance of thermistor against
table in "10-6. Checking Component Parts'
Function".
Compare FTC detected temperature to
hand held detector.
4. Replace board.
1. Visually inspect location and reattach as
necessary.
2. Check resistance of thermistor against
table in "10-6. Checking Component Parts'
Function".
Compare FTC detected temperature to
hand held detector.
3. Replace board.
1. Visually inspect location and reattach as
necessary.
2. Check resistance of thermistor against
table in "10-6. Checking Component Parts'
Function".
Compare FTC detected temperature to
hand held detector.
3. Replace board.
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. Check circulation pump (See "10-6.
Checking 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 flow amount is within the
recommended range.
3. Check valves on primary water circuit are
installed level.
Electrically test to determine fault.
5. Visually check the CN1A connector and
reattach if necessary.
6. Electrically test to determine fault.
See "10-6. Checking Component Parts'
Function" for how to check.
7. Check the SW2-2 setting.
8. Replace board.
1. If more head required either add a pump
of the same size or replace existing pump.
2. Check circulation pump (See "10-6.
Checking 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 flow amount is within the
recommended range.
3. Visually check the IN3 terminal and reat-
tach if necessary.
4. Electrically test to determine fault.
5. Check the SW3-2 setting.
6. Replace board.