Mitsubishi Electric EHST20C-VM6HA Service Manual page 44

10-4. Self diagnosis and action
Check if Dip SW is set correctly. (Refer to Chapter 6-10.)
Error code Title and display conditions
L1 Booster heater overheat detection
<DHW/Heating/LP/FS/OS>
Error code displayed when THW3 detects
temp. of ≥ 85ºC for 10 consecutive seconds.
DHW : Domestic hot water mode
Heating : Heating mode
LP : Legionella prevention mode
FS : Freeze stat
OS : Operation stop
TH1 : Room temp. thermistor
TH2 : Liquid refrigerant temp. thermistor
THW1 : Flow water temp. thermistor
THW2 : Return water temp. thermistor
THW3 : Booster heater temp. thermistor
THW5B : Tank water temp. thermistor
L Booster heater thermistor (THW3) failure
<DHW/Heating/LP/FS>
Error code displayed when THW3 is at open
(≤ 1.31ºC) or short (≥ 219.42ºC).
Exceptions
Error code will not be displayed if;
During defrost and 10 mins after defrost
operation,
For 10 mins after pump1 is switched on,
When THW1 < 10deg.
Possible Cause
Insufficient system head
1
Reduced flow in primary water circuit
2
Due to 1 or more of the following;
Faulty pump, insufficient air purge, blocked-
strainer, leak in water circuit.
3 Valve operation fault
2-way valve (Locally supplied) actuator fault
4
3-way valve actuator fault
5
Booster heater relay (BHC1, BHC2, BHCP)
6
operating fault
Power supply voltage increase
7
8 THW1 has become detached from its holder.
9 THW3 fault
0 FTC3 board failure
Connector/terminal wire has become
1
detached or loose wiring.
2 THW3 fault
3 FTC3 board failure
44
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.
Check circulation pump (See 10-6. for how
2
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.
Check valves on primary water circuit are
3
installed level.
4 Electrically test to determine fault.
1) Electrically test to determine fault.
5
2) Operate 3-way valve manually using
the main remote controller. (Refer to
<Manual operation> in 9.2).
3) Replace 3-way valve coil.
4) Replace 3-way valve. (Refer to Proce-
dure 6 in "11. DISASSEMBLY PROCE-
DURE."
Electrically test the relays (BHC1, BHC2,
6
BHCP) to determine fault.
See 10-6. for how to check
Check the supply voltage.
7
8 Visually inspect location and reattach as
necessary.
Check resistance of thermistor against table
9
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
0 Replace board.
1 Visually check the terminals and connections
and reattach as appropriate.
Check resistance of thermistor against table
2
in section 10-6.
Compare FTC3 detected temperature to
hand held detector.
3 Replace board.