Mitsubishi Electric EHSD-MEC.UK Service Manual page 51

No. Fault symptom
14 In 2-zone tempera- 1. When Zone1 and Zone2 are both in heating
ture control, only mode, the hot water temperature in Zone2
Zone2 does not does not exceed that in Zone1.
reach the set tem-
2. Faulty wiring of motorized mixing valve
perature.
3. Faulty installation of motorized mixing valve
4. Incorrect setting of Running time
5. Motorized mixing valve failure
15 When a PUHZ- The outdoor unit is set to have operation of the
FRP outdoor unit is indoor unit of air conditioner take precedence
connected, DHW or over that of the hydrobox, and in the main control-
Heating operation ler settings "Electric heater (Heating)" or "Electric
cannot run. heater (DHW)" is turned off.
16 When a PUHZ-FRP When the outdoor unit is set to have cooling
outdoor unit is con- operation of the indoor unit of air conditioner take
nected and is in heat precedence over that of the hydrobox, the outdoor
recovery operation, unit controls the frequency of the compressor
the set temperature according to the load of air conditioner. The DHW
is not reached. and heating run according to that frequency.
17 After DHW operation At the end of the DHW mode operation the 3-way
room temperature valve diverts hot water away from the DHW circuit
rises slightly. into space heating circuit.
This is done to prevent the hydrobox components
from overheating.
The amount of hot water directed into the space
heating circuit varies according to the type of the
system and of the pipe run between the plate heat
exchanger and the hydrobox.
The room tempera- 3-way valve failure
18
ture rises during DHW
operation.
19 Water discharges 1. If continual – pressure relief valve may be
from pressure relief damaged.
valve.
(Primary circuit)
2. If intermittent – expansion vessel charge may
have reduced/bladder perished.
20 Water discharges 1. If continual – field supplied pressure reducing
from pressure relief valve not working.
valve (field supplied
2. If continual – pressure relief valve seat may
item).
be damaged.
(Sanitary circuit)
3. If intermittent – expansion vessel charge may
have reduced/bladder perished.
4. DHW tank may have subjected to backflow.
21 Noisy water circula- Air in water circulation pump .
tion pump
22 Noise during hot 1. Loose airing cupboard pipework.
water draw off
typically worse in the
2. Heaters switching on/off.
morning.
23 Mechanical noise 1. Heaters switching on/off.
heard coming from
the hydrobox.
2. 3-way valve changing position between DHW and
heating mode.
24 Water circulation Water circulation pump jam prevention mechanism
pump runs for a (routine) to inhibit the build-up of scale.
short time unexpect-
edly .
25 Milky/Cloudy water Oxygenated water
(Sanitary circuit)
26 Heating mode has The time of "Delay" set in "Economy settings
for pump" is too short. (Go to "Service menu"
been on standby for
→ "Auxiliary settings" → "Economy settings for
a long time (does
pump").
not start operation
smoothly.)
OCH571
Possible cause
51
Explanation - Solution
1. Normal action no action necessary.
2. Refer to "5.3 Wiring for 2-zone temperature control" in installation manual.
3. Check for correct installation. (Refer to the manual included with each mo-
torized mixing valve.)
4. Check for correct setting of Running time.
5. Inspect the mixing valve. (Refer to the manual included with each motorized
mixing valve.)
Turn ON Electric heater (Heating) or Electric heater (DHW) using the main con-
troller.
Normal operation no action necessary.
If Air-to-Water system is given priority in operation, comp Hz can be regulated
depending on the load of DHW or Heating. For more details, refer to the PUHZ-
FRP installation manual.
Normal operation no action necessary.
Check the 3-way valve.
1. Turn the handle on the pressure relief valve to check for foreign objects in it.
If the problem is not still solved, replace the pressure relief valve with a new
one.
2. Check pressure in expansion vessel.
Recharge to 1 bar if necessary.
If bladder perished replace expansion vessel with a new one.
1. Check function of pressure reducing valve and replace if necessary.
2. Turn the handle on the pressure relief valve to check for foreign objects in-
side. If the problem is not still solved, replace the pressure relief valve.
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
pre-charge.
4. Check the 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 wa-
ter supply could flow back to DHW tank. Investigate source of back-feed and
rectify error in pipework/fitting configuration. Adjust pressure in cold supply.
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" .