Mitsubishi Electric EHPT20Q-VM2EA Service Manual page 38

Error code Title and display conditions
P1/L5 Indoor unit temperature thermistor failure
* The thermistors subject to failure can be checked
in "Request code: 567" in "Running information
<DHW/Heating/LP/FS/OS>
Error code displayed when thermistor is at open or
short (see table).
Error code
P1 TH1A/TH1B
THW1
THW2
THW3
L5
THW4
THW5A
THW5B
L6 Circulation water freeze protection
<DHW/Heating/FS/OS>
Error code displayed when THW1 detects a
seconds.
Exception
Error code will not be displayed if;
FS function is disabled,
For 10 minutes after water circulation pump1 is
switched on.
L8 Heating operation error
* "3" 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
(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)
GCH15010
1.
2.
3.
4.
Thermistor
Symbol Name
Room temperature thermisitor
Flow water temperature thermisitor
Return water temperture thermisitor
Flow water temp. thermisitor (to tank)
DHW supply temp. thermistor
Stored water temp. thermistor (upper)
Stored water temp. thermistor (lower)
1.
2. Valve operation fault
3. 2-way valve (local supply) actuator
4. 3-way valve actuator fault
5. THW1 or THW2 has become detached
6. THW1 or THW2 fault
7. FTC board failure
1.
2.
3.
4.
Possible Cause
Connector/terminal wire has become
detached or loose wiring.
Thermistor fault
FTC board failure
The thermistor on the wireless remote
controller or the main remote control-
ler may be defective. (when Room
temp. is chosen for the Heating opera
tion and when Main remote controller
or Room RC 1-8 is chosen for the
Room Sensor setting in the Initial
setting)
Open detection
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
fault
from its holder.
THW1 has become detached from its
holder.
Booster heater fault
THW1 or THW2 fault
FTC board failure
38
Diagnosis and action
1. Visually check the terminals and connec-
tions and reattaches appropriate.
2. Check resistance of thermistor against
table in section 10-6.
Compare FTC detected temperature to
hand held detector.
3. Replace board.
4. Replace wireless remote controller or main
remote controller.
Short detection
Check circulation pump (See 10-6. for how
1.
to check).
Open air vent 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 during heating
operation.
Refer to Procedure 5 in "11. DISASSEMBLY
PROCEDURE."
Check valves on primary water circuit are
2.
installed level.
Electrically test to determine fault
3.
1) Electrically test to determine fault.
4.
2) Operate 3-way valve manually using
the main remote controller. (Refer to
<Manual operation> in 9-4).
3) Replace 3-way valve coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
5. Visually inspect location and reattach as
necessary.
6. Check resistance of thermistor against table
in section 10-6.
Compare FTC detected temperature to
hand held detector.
7. Replace board.
1. Visually inspect location and reattach as
necessary.
2. Electrically test to determine fault.
See 10-6. for how to check.
3. Check resistance of thermistor against
table in section 10-6.
Compare FTC detected temperature to
hand held detector.
4. Replace board.