Mitsubishi Electric EHSD-MED Service Manual page 45

Check code Title and display conditions
P1/P2/L5/LD Indoor unit temperature thermistor failure
Note: The thermistors subject to failure can be
checked in "Request code: 567" in "Running
information.
<DHW/Heating/Cooling/LP/FS/OS>
Check code displayed when thermistor is at open
or short (see table).
Exceptions
Check code will not be displayed for TH2; During
defrost and for 10 minutes after defrost operation.
Check code
Symbol
P1 TH1A/TH1B
P2 TH2
THW1
THW2
THW5A
THW5B
L5
THW6
THW7
THW8
THW9
LD THWB1
Circulation water freeze protection
L6
<DHW/Heating/Cooling/LP/FS/OS>
Check code displayed when THW1 detects
a temp. ≤ 1ºC for 10 consecutive seconds or
THW2 detects a temp. ≤ 3ºC for 10 consecutive
seconds.
Exception
Check code will not be displayed if;
FS function is disabled,
For 10 minutes after water circulation pump1 is
switched on.
OCH712C
Possible Cause
1. Connector/terminal wire has become
detached or loose wiring.
2. Thermistor fault
3. FTC board failure
4. The thermistor on the wireless remote
controller or the main remote controller
may be defective. (when Room temp.
is chosen for the Heating operation
and when Main remote controller or
Room RC 1-8 is chosen for the Room
Sensor setting in the Initial setting)
5. Incorrect setting of the DIP switch(es)
Thermistor
Name
Room temperature thermistor
Liquid temperature thermistor
Flow water temperature thermistor
Return water temperature thermistor
DHW tank water temperature thermistor (upper)
DHW tank water temperature thermistor (lower)
Zone1 flow temperature thermistor
Zone1 return temperature thermistor
Zone2 flow temperature thermistor
Zone2 return temperature thermistor
Boiler flow temperature thermistor
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. 3-way valve (local supply) actuator fault 5.
6. THW1 has become detached from its
holder.
7. THW1 or THW2 fault
8. FTC board failure
45
Diagnosis and action
1. Visually check the terminals and connec-
tions and reattaches appropriate.
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.
4. Replace wireless remote controller or main
remote controller.
5. Check the DIP switch setting(s).
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
−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
−40ºC or below 140ºC or above
1. Refer to table in "10-6. Checking Compo-
nent 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. Check-
ing 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.
1) Electrically test to determine fault.
2) Operate 3-way valve manually using the
main remote controller. (Refer to <Manual
operation> in "9-4. Service Menu".)
3) Replace 3-way valve.
6. Visually inspect location and reattach as
necessary.
7. Check resistance of thermistor against table
in "10-6. Checking Component Parts' Func-
tion".
Compare FTC detected temperature to
hand held detector.
8. Replace board.