Service And Maintenance; Troubleshooting; Maintenance - Mitsubishi Electric EHST20 Series Operation Manual

5

Service and Maintenance

troubleshooting

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
(systems with cylinder)
Water discharges from one of the
relief valves
Small amounts of water drip from
one of the relief valves.
Noisy pipework
Heating system does not get up
to set temperature.
An error code appears in the
main controller display.
Pump runs without reason for
short time.
Mechanical noise heard coming
from cylinder unit
After DHW operation room tem-
perature rises a little.
Schedule function inhibits the
system from operating but the
outdoor unit operates.
H e a t i n g m o d e h a s b e e n o n
standby for a long time (does not
start operation smoothly.)
Heating emitter is hot in the DHW
mode. (The room temperature
rises.)
<Power failure>
All setting will be saved for  week with no power, after  week Date/Time ONLY will be saved.

Maintenance

Maintenance to the cylinder and hydrobox should be carried out annually by a competent person only. Users should not try to service or replace parts of the cylinder or hyd-
robox themselves. Failure to observe this instruction could result in injury to the user, damage to the unit and the product warranty becoming invalid.
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.
Parts which require regular replacement
Parts replace every
Pressure relief valve (PRV)
Air vent (Auto/Manual)
Drain cock (Primary circuit)
6 years
Flexible hose
Manometer
Inlet control group (ICG)*
*
OPTIONAL PARTS for UK
3
Possible cause
Scheduled control off period
All hot water from tank used
Heat pump or electric heaters not working
The system has overheated/overpressurised
Dirt may be preventing a tight seal in the valve
Air trapped in the system
Loose pipework
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
The indoor or outdoor unit is reporting an abnormal condi-
tion
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.
At the end of the DHW mode operation the 3-way valve
diverts hot water away from the cylinder into space heat-
ing circuit. This is done to prevent the cylinder unit compo-
nents 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.
Freeze stat. function is active.
Duration is set to excessively short time at "Economy set-
ting for pump".
The 3-way valve may have foreign objects in it, or hot wa-
ter may flow to the heating side due to malfunctions.
Possible failures
Water leakage due to
copper corrosion
(Dezincification)
Solution
Check schedule settings and alter if necessary.
Ensure DHW mode is operating and wait for tank to re-heat.
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.
Try bleeding radiators (if present) If the symptoms persist contact installer.
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.
Make a note of the error code number and contact installer.
Normal operation no action necessary.
Normal operation no action required.
Normal operation no action necessary.
Normal operation no action necessary.
Normal operation no action necessary.
Contact installer.
Contact installer.
Parts which require regular inspection
Parts Check every
Immersion heater 2 years
Pump 20,000 hrs (3 years)
Parts which must not be reused when servicing
* O-ring
* Gasket
note: always replace the gasket for pump with a new one at each regular
maintenance (every 20,000 hours of use or every 3 years).
Possible failures
Earth leakage causing
circuit breaker to activate
(Heater is always OFF)
Pump failure