No.
Fault symptom
Possible cause
Explanation - Solution
12 Heating system does
not get up to set tem-
perature.
1. Prohibit, schedule timer or holiday mode selected.
1. Check settings and change as appropriate.
2. Check settings and change as appropriate.
2. Check the battery power and replace if
fl
at.
3. The room in which the temperature sensor is located is at a
different temperature to the rest of the house.
3. Reposition the temperature sensor to a more suitable room.
4. Heat pump not working.
4. Check heat pump – consult outdoor unit service manual.
5. Booster heater cut out has triggered.
5. Check booster heater thermostat and press reset button if
safe.
Reset button is covered with white rubber cap see component
parts diagram section 10-6. for position.
6. Booster heater breaker (ECB1) has tripped.
6. Check the cause of the trip and reset if safe.
7. The booster heater thermal cut-out has operated and can
not be reset using the manual reset button.
7. Check the resistance of the thermal cut out, if 0 then the
connection is broken and the booster heater will have to be
replaced.
Please contact your Mitsubishi Electric dealer.
8. Incorrectly sized radiators
8. Contact installer
9. 3-way valve (2-way valve) (
fi
eld supply) fault
9. Check plumbing/wiring to 3-way valve (2-way valve) (
fi
eld
supply).
10. Battery problem *wireless control only
10. Check the battery power and replace it
fl
at.
13 After DHW operation
room temperature
rises a little.
At the end of the DHW mode operation the 3-way valve (2-way
valve) (field supply)diverts hot water away from the hydrobox
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
is dependent on the type of system and the pipe run between
the plate heat exchanger and the hydrobox.
Normal operation no action necessary.
14 The room temperature
rises during DHW
operation.
3-way valve (2-way valve) (
fi
eld supply) fault
Check the 3-way valve (2-way valve) (
fi
eld supply).
15 Water discharges from
pressure relief valve.
(Primary circuit)
1. If continual – pressure relief valve seat may be damaged.
1. Remove cartridge – check seat and renew if necessary.
2. If intermittent – expansion vessel charge may have
reduced/bladder perished.
2. Check pressure in expansion vessel.
Recharge to 1 bar if necessary.
If bladder perished replace vessel.
3. System was excessively pressurised at
fi
ll stage.
3. Ensure the
fi
ll connection has been physically DISCONNECT-
ED from the mains water supply. With hydrobox cold check
pressure in hydrobox. If necessary, discharge/re-
fi
ll system to
the recommended cold-
fi
ll pressure of 1 bar.
4. Unit has overheated – thermal controls have failed.
4. Switch off power to the heat pump. Leave water supply on.
Wait until discharge stops. Isolate water supply and replace if
faulty.
16 Water discharges from
pressure relief valve.
(Sanitary circuit)
1. If continual –
fi
eld supplied pressure reducing valve not working.
1. Check function of pressure reducing valve and replace if
necessary.
2. If continual – pressure relief valve seat may be damaged.
2. Remove cartridge – check seat and renew if necessary.
3. Check pressure in expansion vessel.
Recharge to correct precharge pressure if necessary.
If bladder perished replace vessel.
3. If intermittent – expansion vessel charge may have
reduced/bladder perished.
4. Unit is being back pressurised.
4. With cylinder cold, check pressure in cylinder. If this is the
same as the incoming mains pressure then you are getting
back feed. Install a balanced cold supply.
18 Noisy pump
Air in pump.
Use manual and automatic air vents to release excess air from
system. Top up water if necessary to achieve 1bar on primary
circuit.
19 Noise during hot water
draw off typically
worse in the morning.
Loose airing cupboard pipework.
Heaters switching on/off.
Install extra pipe fastening clips.
20 Mechanical noise
heard coming from the
hydrobox.
1.
Heaters switching on/off.
Normal operation no action necessary.
2.
3-way valve (
fi
eld supply) changing position between DHW
and heating mode.
21 Pump runs for a short
time for no reason.
Pump jam prevention mechanism to inhibit the build up of scale. Normal operation no action necessary.
22 Milky/Cloudy water
(Sanitary circuit)
Oxygenated water
Water from any pressurised system will release oxygen bubbles
when
fl
owing. The bubbles will settle out.
23 Heating mode has been
on standby for a long
time (does not start
operation smoothly.)
Duration is set to excessively short time at “Economy setting for
pump”. (Go to “Service menu”
→
“Auxiliary setting”
→
“Economy
setting for pump”).
Set “Economy setting for pump” longer.
24 Heating emitter is hot
in the DHW mode.
(The room temperature
rises.)
1.
The 3-way valve may have foreign objects in it, or hot
water may
fl
ow to the heating side due to malfunctions.
1.
Manually override the 3-way valve several times to check
whether the problem will be solved. (Refer to the service
manual.) If the problem persists replace the 3-way valve coil
with a new one. If still no change replace the entire 3-way
valve with a new one.
2.
2-way valve (
fi
eld supply) has tripped.
2.
Check the cause of the trip and check plumbing/wiring to
2-way valve (
fi
eld suppl).
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