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7
Water to Water Heat Pump (WTW)
Annual Maintenance
It is essential that the heat pump is serviced at least once a year by a qualified individual. Any required parts 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.
Note:
Within the first couple of months of installation, remove and clean the heat pump unit's strainer plus any additional
filter items that are fitted external to the heat pump unit. This is especially important when installing on an old/exist-
ing pipe work system.
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 only by a competent per-
son with relevant training and qualifications.
Parts which require regular replacement
Parts
Pressure relief valve (PRV)
Manometer
<Draining the heat pump unit and its primary heating circuit (local)>
WARNING: DRAINED WATER MAY BE VERY HOT
1. Firstly to eliminate any air in heat pump unit pipe works, engage the DHW pump circulator for 1-2 mins and expel any trapped
air via nearest hot water tap so as unit becomes fully primed/water charged.
2. Before attempting to drain the heat pump unit isolate from the electrical supply to prevent the immersion and booster heaters
burning out.
3. Isolate cold water feed to DHW tank.
4. Open a hot water tap to start draining without a vacuum.
5. Attach a hose to the DHW tank drain cocks. 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.
6.When the DHW tank is drained close drain cock and the hot water tap.
7. Attach hose to water circuit drain cocks (No. 7 on Figure 7.5.1). 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 booster heater drain cock to encourage siphoning.
Open the pump valves and the strainer valves.
8. Water remains in the strainer still after the heat pump unit was drained.
Drain the strainer by removing the strainer cover.
Replace
Possible failures
every
6 years
Water leakage
<Figure 7.8.1>
Parts which require regular inspection
Parts
Check every
1 year
Pressure relief
(turning the
valve (3 bar)
knob manually)
Immersion heater 2 years
Water circulation
20,000 hrs
pump
(3 years)
(Primary circuit)
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).
Drain cock (DHW tank)
Possible failures
PRV would be fixed
and expansion vessel
would burst
Earth leakage causing
circuit breaker to acti-
vate (Heater is always
OFF)
Water circulation pump
failure
B-263
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