Service And Maintenance; Basic Troubleshooting For Cylinder Unit - Mitsubishi Electric ecodan EHST20 Série Manuel D'installation

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Service and Maintenance

The indoor cylinder unit is UNVENTED. Under UK law* the system must be
serviced once a year by a qualified individual. Servicing and maintenance of the
outdoor unit should only be done by a Mitsubishi Electric trained technician with
relevant qualifications and experience. Any electrical work should be done by a
tradesperson with the appropriate electrical qualifications. Any maintenance or

Basic troubleshooting for Cylinder Unit

The following table is to be used as a guide to possible problems. It is not exhaustive and all problems should be investigated by the installer or another competent person.
Users should not attempt to repair the system themselves.
At no time should the system be operating with the safety devices by-passed or plugged.
Fault symptom
Cold water at taps
Heating system does not get up
to set temperature.
After DHW operation room tem-
perature rises a little.
Heating emitter is hot in the DHW
mode. (The room temperature
rises.)
Schedule function inhibits the
system from operating but the
outdoor unit operates.
Pump runs without reason for
short time.
Mechanical noise heard coming
from cylinder unit
Noisy pipework
Water discharges from one of the
relief valves
Small amounts of water drip from
one of the relief valves.
An error code appears in the
main controller display.
<Power failure>
All setting will be saved for 1 week with no power, after 1 week Date/Time ONLY will be saved.
For more details, refer to the service manual.
<draining the cylinder unit and its primary heating circuit (local)>
WArninG: drAined WAter MAy Be Very HOt
1. Before attempting to drain the cylinder unit isolate from the electrical supply to prevent the immersion and booster heaters burning out.
2. Isolate cold water feed to DHW tank.
3. Attach a hose to the DHW tank drain cock (No. 17 on Figure 3.1 - 3.4). The hose should be able to withstand heat as the draining water could be very hot. The hose
should drain to a place lower than the DHW tank bottom to encourage siphoning.
Open a hot water tap to start draining without a vacuum.
4. When the DHW tank is drained close drain cock and hot tap.
5. Attach hose to booster heater drain cock and water circuit drain cock (No. 13 and No. 16 on Figure 3.1 - 3.4). The hose should be able to withstand heat as the drain-
ing water could be very hot. The hose should drain to a place lower than the booster heater drain cock to encourage siphoning. Open the pump valves and the strainer
valves.
6. Water remains in the strainer still after the cylinder unit was drained.
Drain the strainer by removing the strainer cover.
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Possible cause
Scheduled control off period
All hot water from DHW tank used
Heat pump or electric heaters not working
Prohibit, schedule or holiday mode selected
Incorrectly sized radiators
The room in which the temperature sensor is located is at
a different temperature to the rest of the house.
Battery problem *wireless control only
At the end of the DHW mode operation the 3-way valve
diverts hot water away from the DHW tank into space
heating circuit. This is done to prevent the cylinder unit
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 cylinder unit.
The 3-way valve may have foreign objects in it, or hot wa-
ter may flow to the heating side due to malfunctions.
Freeze stat. function is active.
Pump jam prevention mechanism to inhibit the build up of
scale.
Heaters switching on/off
3-way valve changing position between DHW and heating
mode.
Air trapped in the system
Loose pipework
The system has overheated or overpressurised
Dirt may be preventing a tight seal in the valve
The indoor or outdoor unit is reporting an abnormal condi-
tion
'DIY' fixes done by a non-accredited person could invalidate the Warranty and/or
result in damage to the cylinder unit and injury to the person.
* Building regulations – England & Wales Part G3, Scotland P3, Northern Ireland
P5. If outside of the UK please refer to local building regulations regarding un-
vented hot water storage.
Solution
Check schedule settings and change if necessary.
Ensure DHW mode is operating and wait for DHW tank to re-heat.
Contact installer.
Check settings and change as appropriate.
Contact installer.
Reposition the temperature sensor to a more suitable room.
Check the battery power and replace if flat.
Normal operation no action necessary.
Contact installer.
Normal operation no action necessary.
Normal operation no action necessary.
Normal operation no action required.
Normal operation no action necessary.
Try bleeding radiators (if present) If the symptoms persist contact installer.
Contact installer.
Switch off power to the heat pump and any immersion heaters then con-
tact installer.
Twist the valve cap in the direction indicted until a click is heard. This will
release a small amount of water flushing dirt from the valve. Be very care-
ful the water released will be hot. Should the valve continue to drip contact
installer as the rubber seal may be damaged and need replacing.
Make a note of the error code number and contact installer.