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Service And Maintenance - Mitsubishi Electric ecodan EHPT20Q-VM2EA Installation Manual

Cylinder unit
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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
Possible cause
Cold water at taps
System or power input is OFF.
DHW is scheduled "OFF"
All reserves of hot water from thermal store tank have been
Heat pump or booster heater not working
Air exists within pump A
Flow sensor jam / defect
Supply flow rate is low
Heating system does not get up
Prohibit, schedule or holiday mode selected
to set temperature.
Incorrectly sized radiators or low flow rate setting
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
Heat emitter is hot in the DHW
The 3-way valve may have foreign objects in it, or hot
mode. (The room temperature
water may flow to the heating side due to abnormal
Schedule function inhibits the
Freeze stat function may be active, to prevent freezing.
system from operating but the
outdoor unit is operational.
Pump runs without reason for
Pump jam prevention control routine to inhibit the build up
short time.
of scale.
Mechanical noise (minor) heard
Booster heater switching on/off
coming from cylinder unit
Pump operates during hot water supply
3-way valve changing position between DHW and heating
Abnormal cylinder noise during
Air present in pump A
delivery of domestic hot water
Noisy pipework
Air trapped in the system
Loosely supported pipe work.
Water discharges from one of the
The system has overheated or overpressurised
pressure relief valves
Small amounts of water drip from
Dirt may be preventing proper tight seal in the valve
one of the pressure relief valves.
An error code appears in the
The indoor or outdoor unit is reporting an abnormal
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)>
1.Before attempting to drain the cylinder unit isolate from the electrical supply to prevent the booster heaters burning out.
When the ECB is turned off, push down the power lever without pressing the test button.
2.Isolate cold water feed to secondary (potable) circuit.
3.Attach a hose to the drain cock (No.4 on the front side of heat exchanger shown in Figure 3. 2).*1
Open a hot water tap to start draining without a vacuum.
Open the drain cock of the heat exchanger .
4.When the secondary (potable) circuit is drained close drain cock and hot tap.
5.Draining procedure of the thermal store tank (primary circuit) is as follows.
(1) Open the cap of the pressure relief valve to reduce the pressure of the thermal store tank to 0 bar.
(2) Attach a hose to the manual air vent (No. 12 above the thermal store tank shown in Figure 3.2).*1
Open the manual air vent.
(3) Check that the pump valves and the strainer valve are opened.
Open the drain valve (No.13 shown in Figure 3. 2) to drain the water in the thermal store tank.
(4) Open all other drain cocks. (No.3 shown in Figure 3.2 and drain cocks of outdoor unit)
(5) Water remains in the strainer still after the cylinder unit was drained. Drain the strainer by removing the strainer cover.
*1. The hose should be able to withstand heat as the draining water could be very hot.
'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.
Turn on the power/system.
Check schedule settings and change if necessary.
Ensure DHW mode is operating and wait for thermal store tank to re-heat.
Contact installer.
Open the air vent above pump A (refer to page 12).
Contact installer.
Increase the delivery amount. (open tap further.)
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.
Contact installer.
Normal operation no action necessary.
Normal operation no action necessary.
Normal operation no action required.
Normal operation no action necessary.
Normal operation no action necessary.
Open the air vent above pump A (refer to page 12). If the symptoms
persist contact installer.
Try bleeding radiators (if present) If the symptoms persist contact installer.
Contact installer.
Switch off power to the cylinder unit and the booster heater then contact
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 careful
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 plus any other observation(s) and
contact installer.
Circulation water temperature overheat protection
Thermal store tank water temperature overheat protection
Indoor unit temperature thermistor (THW1, THW2, THW3, THW4, THW5A,
THW5B) failure
Circulation water freeze protection
Heating operation error
Low primary circuit flow rate detected by flow sensor (flow sensors1,B)
Flow sensor failure (flow sensors1,A,B)
DHW supply temperature overheat protection
Water ciculation pump failure
Communication failure between FTC and wireless receiver
Thermistor (Room temp.) (TH1) failure
J1 - J8
Communication failure between wireless receiver and wireless remote controller
E0 - E5
Communication failure between main controller and FTC
E6 - EF
Communication failure between FTC and outdoor unit
U*, F*
Outdoor unit failure
It is essential that the cylinder unit is serviced at least once a year by a qualified individual. Any spare parts required should be purchased from Mitsubishi Electric.
Never bypass safety devices or operate the unit without them being fully operational. For more details, refer to service handbook.
In addition to annual servicing it is necessary to replace or inspect some parts after a certain period of system operation. Please see tables below for detailed instructions.
Replacement and inspection of parts should always be done by a competent person with relevant training and qualifications.
Pressure relief valve (PRV)
Air vent (Auto)
6 years
Water leakage
Flow rate may be reduced check for;
primary circuit, complete filling and reset error code.)
Check resistance across the thermistor (THW1,THW3, THW5A).
Check resistance across the thermistor.
See Action for L3.
Re-attach any thermistors that have become dislodged.
See Action for L3. If the flow sensor itself does not work,replace it.
Discharge the air for primary circuit.
Turn on the pump A and pump 1 using Manual operation to flush debris
on the flow sensor.
Check flow sensor cable for damage or loose connections.
See Action for L3.
Check detection value of thermistor is the same as the actual temperature
Check resistance across the thermistor (Cylinder unit and outdoor unit)
Check cloggings of the pump with foreign materials
Check water circulation pump cable for damage or loose connections.
Check connection cable for damage or loose connections.
Check resistance across the thermistor.
Check the room sensor settings.(page 26)
Check wireless remote controller's battery is not flat.
Check the pairing between wireless receiver to wireless remote controller.
Test the wireless communication. (See the manual of wireless system)
Check connection cable for damage or loose connections.
Check that the outdoor unit has not been turned off.
Check connection cables for damage and miswiring or loose connections.
Press the reset button and recover the system after lowering the tempera-
ture if the thermostat of outdoor unit operates.
Refer to outdoor unit service manual.
Refer to outdoor unit service manual.
Water circulation pump
Water circulation pump1
50,000 hrs (7 years)
* O-ring
* Gasket

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