Self Diagnosis And Action; Circulation Water Temperature Overheat Protection; Tank Water Temperature Overheat Protection - Mitsubishi Electric EHST17D-VM2D Service Manual

10-4. Self diagnosis and action

Check if DIP SW is set correctly. (Refer to "6-6. DIP switch functions".)
Error code Title and display conditions
L3 Circulation water temperature overheat
protection
<DHW/Heating/Cooling/LP/FS/OS>
Error code displayed when THW1 detects a
temp. ≥ 80ºC for 10 consecutive seconds or
THW2 detects a temp. ≥ 80ºC for 10 consecutive
seconds.
DHW : Domestic hot water mode
Heating : Heating mode
Cooling : Cooling mode
LP : Legionella prevention mode
FS : Freeze stat
OS : Operation stop
TH1A/B : Room temp. thermistor
TH2 : Liquid refrigerant temp. thermistor
THW1 : Flow water temp. thermistor
THW2 : Return water temp. thermistor
THW5B : Tank lower water temp. thermistor
THW6 : Zone1 flow water temperature thermistor
THW7 : Zone1 return water temperature thermistor
THW8 : Zone2 flow water temperature thermistor
THW9 : Zone2 return water temperature thermistor
THWB1 : Boiler flow water temperature thermistor
L4

Tank water temperature overheat protection

<DHW/Heating/Cooling/LP/FS/OS>
Error code display when THW5B detects a
temp. ≥ 75ºC for 10 consecutive seconds.
OCH714A
Possible Cause
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
5. 3-way valve actuator fault
6. Booster heater relay (BHC1, BHC2,
BHCP) operating fault
7. Power supply voltage increase
8. THW1 or THW5 has become de-
tached from its holder.
9. THW1 or THW2 fault
10. FTC board failure
1. 3-way valve actuator fault
2. Immersion heater relay (IHC) operat-
ing fault
3. THW5B fault
4. FTC board failure
49
Diagnosis and action
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. 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.
4. Electrically test to determine fault
5. 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 coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
6. Electrically test the relays (BHC1, BHC2,
BHCP) to determine fault.
See "10-6. Checking Component Parts'
Function" for how to check.
7. Check the supply voltage.
8. Visually inspect location and reattach as
necessary.
9. Check resistance of thermistor against
table in "10-6. Checking Component Parts'
Function".
Compare FTC detected temperature to
hand held detector.
10. Replace board.
1. 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 coil.
4) Replace 3-way valve. (Refer to Procedure
6 in "11. DISASSEMBLY PROCEDURE."
2. Check immersion heater relay (IHC).
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.