Indoor Unit Temperature Thermistor Failure; Circulation Water Freeze Protection - Mitsubishi Electric EHSC-VM2B Service Manual

Error code Title and display conditions
P1/P2/L5/LD

Indoor unit temperature thermistor failure

* The thermistors subject to failure can be
checked in "Request code: 567" in "Running
information
<DHW/Heating/Cooling/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.
Error code
Symbol
P1 TH1A/TH1B
P2 TH2
THW1
THW2
THW5
L5 THW6
THW7
THW8
THW9
THWB1
LD
THWB2
L6

Circulation water freeze protection

<DHW/Heating/Cooling/LP/FS/OS>
Error code displayed when THW1 detects a
temp. ≤ 1ºC for 10 consecutive seconds or
THW2 detects a temp. ≤ 3ºC for 10 consecutive
seconds.
Exception
Error code will not be displayed if;
FS function is disabled,
For 10 mins after water circulation pump1 is
switched on.
OCH532A
1. Connector/terminal wire has become
detached or loose wiring.
2. Thermistor fault
3. FTC4 board failure
4. The thermistor on the wireless remote
controller or the main remote control-
ler may be defective. (when Room
temp. is chosen for the Heating op-
eration and when Main 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
Tank water temperature thermistor
Zone 1 fl ow water temperature thermistor
Zone 1 return water temperature thermistor
Zone 2 fl ow water temperature thermistor
Zone 2 return water temperature thermistor
Boiler flow water temperature thermistor
Boiler return water temperature thermistor
1. Insuffi cient system head
2. Reduced fl ow in primary water circuit.
Due to 1 or more of the following;
Faulty pump, insufficient air purge,
blockedstrainer, leak in water circuit.
3. Valve operation fault
4. 2-way valve (fi eld supply) actuator fault
5. 3-way valve actuator fault
6. THW1 has become detached from its
holder.
7. THW1 or THW2 fault
8. FTC4 board failure
53
Possible Cause
1.
2.
3.
4.
5.
Open 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
-40ºC or below 140ºC or above
-40ºC or below 140ºC or above
1. Refer to table in section 10-6. to determine
2. Check circulation pump (See 10-6. for how
3. Check valves on primary water circuit are
4. Electrically test to determine fault.
5. 1) Electrically test to determine fault.
6. Visually inspect location and reattach as
7. Check resistance of thermistor against table
8. Replace board.
Diagnosis and action
Visually check the terminals and connec-
tions and reattachas appropriate.
Check resistance of thermistor against ta-
ble in section 10-6.
Compare FTC4 detected temperature to
hand held detector.
Replace board.
Replace wireless remote controller or main
remote controller
Check the Dip switch setting(s).
Short detection
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.
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.
installed level.
2) Operate 3-way valve manually using the
main remote controller. (Refer to <Manu-
al operation> in 9.2).
3) Replace 3-way valve coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
necessary.
in section 10-6.
Compare FTC4 detected temperature to
hand held detector.