Self Diagnosis And Action; Circulation Water Temperature Overheat Protection; Tank Water Temperature Overheat Protection - Mitsubishi Electric EHSD-MEC.UK Service Manual

10-4. Self diagnosis and action

Check if DIP SW is set correctly. (Refer to Section 6-6.)
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 temperature thermistor
TH2 : Liquid refrigerant temperature thermistor
THW1 : Flow water temperature thermistor
THW2 : Return water temperature thermistor
THW5 : Tank water temperature thermistor
THW6 : Zone 1 flow water temperature thermistor
THW7 : Zone 1 return water temperature thermistor
THW8 : Zone 2 flow water temperature thermistor
THW9 : Zone 2 return water temperature thermistor
THWB1 : Boiler flow water temperature thermistor
THWB2 : Boiler return water temperature thermistor
L4

Tank water temperature overheat protection

<DHW/Heating/Cooling/LP/FS/OS>
Error code display when THW5 detects a
temp. ≥ 75ºC for 10 consecutive seconds.
OCH571
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,
blockedstrainer, leak in water circuit.
3. Valve operation fault
4. 2-way valve (local supply) actuator
fault
5. 3-way valve (local supply) 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 (local supply) actuator
fault
2. Immersion heater relay (IHC) operat-
ing fault
3. THW5 fault
4. FTC board failure
42
Diagnosis and action
1. Refer to table in section 10-6. to determine 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.
2. 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 rec-
ommended 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).
3) Replace 3-way valve.
6. Electrically test the relays (BHC1, BHC2,
BHCP) to determine fault.
See 10-6. 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 section 10-6.
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).
3) Replace 3-way valve.
2. Check immersion heater relay (IHC)
3. Check resistance of thermistor against table
in section 10-6.
Compare FTC detected temperature to hand
held detector.
4. Replace board.