Mitsubishi EHST20C-VM2C Service Manual page 73

No. Fault symptom
22 Water discharges from 1.
expansion relief valve
- part of Inlet Control
2.
Group
(EH*T20*-MHCW only)
(sanitary circuit)
3.
4.
5.
23 Noisy water circulation Air in water circulation pump.
pump
24 Noise during hot water 1.
draw off typically
worse in the morning.
2.
25 Mechanical noise 1.
heard coming from the
cylinder unit.
2.
26 Water circulation pump Water circulation pump jam prevention mechanism
runs for a short time (routine) to inhibit the build-up of scale.
unexpectedly.
27 Milky/Cloudy water Oxygenated water
(Sanitary circuit)
28 Heating mode has
The time of "Delay" set in "Economy settings
been on standby for for pump" is too short. (Go to "Service menu"
a long time (does → "Auxiliary settings" → "Economy settings for
not start operation pump").
smoothly.)
29 The cylinder unit The cylinder unit is designed to run in an operation
that was running in mode with a higher priority (i.e. DHW mode in this
the heating mode
case) at power recovery.
before power failure
is running in the DHW
mode after power
recovery.
30 Cooling mode is NOT DIP SW2-4 is OFF.
available.
31 The cooling system 1. When the water in the circulation circuit is un-
duly hot, Cooling mode starts with a delay for
does not cool down to
the protection of the outdoor unit.
the set temperature.
2. When the outdoor ambient temperature is
lower than the preset temperature that acti-
vates the freeze stat function, Cooling mode
does not start running.
32 The electric heaters are The setting time period of Heat-pump-only opera-
tion is short.
activated shortly after
DHW or LP mode starts
running after Cooling
mode.
33 During DHW or LP The unit runs in Cooling mode when the outdoor
ambient temperature is lower than 10ºC (outside
mode following the
of the guaranteed operating range).
cooling mode, error
(When defrosting operation is running at such a
L6 (circulation water
low outdoor ambient temperature after Cooling
freeze protection error )
mode is switched to DHW or LP mode, the water
occurs and the system
temperature in the cooling circuit drops too low,
stops all the operations.
which could result in L6 error to stop all the opera-
tions.
OCH570C
Possible cause
If continual – field supplied pressure
reducing valve not working.
If continual – expansion relief valve may be
damaged.
If intermittent – expansion vessel charge
may have reduced/bladder perished.
DHW tank may have subjected to backflow.
Unit has overheated – thermal controls have
failed.
Loose airing cupboard pipework.
Heaters switching on/off.
Heaters switching on/off.
3-way valve changing position between
DHW and heating mode.
1. Check function of pressure reducing valve and replace if necessary.
2. Turn the handle on the expansion relief valve to check for foreign objects
inside. If the problem is not still solved, replace the expansion relief valve
with a new one.
3. Check gas-side pressure in expansion vessel.
Recharge to correct precharge pressure if necessary.
If bladder perished replace expansion vessel with a new one with
appropriate precharge.
4. Check pressure in DHW tank. If pressure in DHW tank is similar to that in
the incoming mains, cold water supply that merges with incoming mains
water supply could flow back to DHW tank. Investigate source of back-
feed and rectify error in pipework/fitting configuration. Adjust pressure in
cold supply.
5. Switch off power to the heat pump and immersion heaters. Leave water
running. Wait until discharge stops. Isolate water supply and replace if
faulty.
Use manual and automatic air vents to remove air from system.
Top up water if necessary to achieve 1 bar on primary circuit.
1. Install extra pipe fastening clips.
2. Normal operation no action necessary.
Normal operation no action necessary.
Normal operation no action necessary.
Water from any pressurised system will release oxygen bubbles when water is
running. The bubbles will settle out.
Increase the time of "Delay" in "Economy settings for pump" .
• Normal operation.
• A fter the DHW max. operation time has elapsed or the DHW max. temperature
has been reached, the DHW mode switches to the other mode (ex. Heating
mode).
Turn DIP SW2-4 to ON. (Refer to "6-19. DIP switch functions".)
1. Normal operation.
2. To run Cooling mode overriding the freeze stat function, adjust the preset
temperature that activates the freeze stat function.
(Refer to "<Freeze stat function>" on Page 49.)
Adjust the setting time period of Heat-pump only operation. (Refer to "<Electric
heater (DHW)> on Page 47.
Do not run Cooling operation when the outdoor ambient temperature is lower
than 10ºC.
To automatically stop or recover only Cooling operation and keep other opera-
tions running, the freeze stat function can be used. Set the preset temperature
that activates the freeze stat function to adjust the outdoor ambient tempera-
ture as follows. (Refer to "<Freeze stat function>" on Page 49.)
Outdoor ambient temperature
3ºC higher than the preset temperature
5ºC higher than the preset temperature
73
Explanation - Solution
Cooling operation
Stop
Recover