Mitsubishi Electric EHST20C-VM6HB Service Manual page 57

Error code Title and display conditions
Low primary circuit (Zone2 side) flow rate
L9
detected by flow switch
* "" is displayed in "Request code: 569" in "Run-
ning information".
LC
Boiler circulation water temperature overheat
protection
<DHW/Heating/LP/FS/OS>
Error code displayed when THWB1 detects
a temp. ≥80ºC for 10 consecutive seconds or
THWB2 detects a temp. ≥80ºC for 10 consecu-
tive seconds
LD Boiler temperature thermistor (THWB1, THWB)
failure
LE Boiler operation error
<Heating>
Boiler is running and THW6 detects a
temperature <30ºC for consecutive 60 minutes.
Boiler circulation water freeze protection
LH
Setting errors of Dip switches on FTC4 control
LL
board
P1 Indoor unit temperature thermistor (TH1) failure
P Indoor unit temperature thermistor (TH) failure
Anti-freeze protection of plate heat exchanger
P6
<Defrosting>
THW2 detects a temperature ≤15ºC and TH2
detects a temperature ≤−16ºC for consecutive 10
seconds.
OCH531
Possible Cause
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 SW3-3
5.
FTC4 board failure
6.
1. The set temperature for Boiler is too
high.
. Flow rate of the heating circuit from the
boiler may be reduced.
Refer to error codes (P1/P/L5/LD).
1. THW6 has become detached from its
holder.
. Incorrect wiring between FTC4
(OUT10) and the boiler.
. Boiler fuel has run out or the system is
OFF.
4. Boiler failure
5. FTC4 board failure
Flow rate of the heating circuit from the
boiler may be reduced.
Incorrect setting of Dip switches.
1. Boiler operation
. 2-zone temperature control
Refer to error codes (P1/P/L5/LD).
Refer to error codes (P1/P/L5/LD).
1. Reduced water flow
• Clogged filter
• Leakage of water
Low temperature
.
• Low load
• Inlet water is cold
Defective water pump
.
Leakage or shortage of refrigerant
4.
Malfunction of linear expansion valve
5.
57
Diagnosis and action
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 IN7 terminal and reat-
tach if necessary.
4. Electrically test to determine fault.
Check the SW3-3 setting.
5.
6. Replace board.
1. Check if the set temperature for Boiler
for heating exceeds the restriction. (See
the manual for the thermistors "PAC-
TH011HT-E")
. Check for
water leakage
•
strainer blockage
•
water circulation pump function.
•
1. Visually inspect location and reattach as
necessary.
. See the manual of the thermistors "PAC-
TH011HT-E".
. Check the status of the boiler.
4. Check the status of the boiler.
5. Replace board.
Check for
water leakage
•
strainer blockage
•
water circulation pump function.
•
1. For boiler operation, check that Dip SW1-1 is
set to ON (With Boiler) and Dip SW-6 is set
to ON (With Mixing Tank).
. For 2-zone temperature control, check Dip
SW2-7 is set to ON (2-zone) and Dip SW2-6
is set to ON (With Mixing Tank).
1. and .
Check water piping.
. Check water pump.
4. Correct to proper amount of refrigerant.
5. Check linear expansion valve.