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Maintenance
Maintenance Requirements
Unvented hot water systems have a continuing
maintenance requirement in order to ensure safe
working and optimum performance. It is essential
that the relief valve(s) are periodically inspected
and manually opened to ensure no blockage has
occurred in the valves or discharge pipework.
Cleaning of the strainer element and replacement of
the air in the internal air bubble will help to prevent
possible operational faults.
The maintenance checks described below should be
performed by a competent person on a regular basis,
e.g. annually to coincide with boiler maintenance.
After any maintenance, please complete the relevant
Service Interval Record section of the Benchmark
Checklist on page 22 of this manual.
Inspection
The lower immersion boss can be used as an access
point for inspecting the cylinder internally.
Safety Valve Operation
Manually operate the temperature/pressure relief valve
for a few seconds. Check water is discharged and that it
flows freely through the tundish and discharge pipework.
Check valve re-seats correctly when released.
NOTE: Discharged water may be very hot!
Repeat the above procedure for the expansion relief
valve.
Strainer
Turn off the cold water supply, boiler and boost immersion
heaters and any additional heat sources. The lowest
hot water tap should then be opened to de-pressurise
the system. Remove the pressure reducing cartridge
to access the strainer mesh. Wash any particulate
matter from the strainer under clean running water.
Re-assemble ensuring the seal is correctly fitted. DO
NOT use any other type of sealant.
De-scaling Immersion Heaters
Before removing the immersion heater the unit must be
drained. Before draining ensure the water, electrical
supply and Heat Pump have been hydraulically and
electrically isolated. Attach a hose pipe to the drain
valve. The pipe should have sufficient length to drain
water to a suitable discharge point below the level of
the unit. Open a hot tap close to the unit and open
drain valve to drain the cylinder.
the immersion heater housing and disconnect wiring
from immersion heater. Carefully remove the thermostat
capillaries. Note the order of the capillaries within the
pocket.
Remove the cover to
Undo the back nut with the tools supplied and remove
the immersion, taking note of the orientation. Carefully
remove any scale from the surface of the element. DO
NOT use a sharp implement to remove scale as it may
damage the element surface. Ensure sealing surfaces
are clean and seals are undamaged. If in doubt fit a
new gasket (part number 70 351 68).
Replace immersion heater ensuring the leg is pointing
downwards for the lower immersion - it may be helpful
to support the immersion heater using a round bladed
screwdriver inserted into one of the thermostat pockets
whilst the back nut is tightened. Replace thermostat
capillaries into pockets. Connect wiring to element.
Check, close and secure the immersion heater housing
cover.
If necessary the temperature can be adjusted by
inserting a flat bladed screwdriver in the adjustment
knob on front of the immersion heater thermostat and
rotating. The adjustment represents a temperature
range of 12 to 72 °C. Check the operation of
thermostat(s) and that no water has discharged from
the expansion relief valve or temperature/pressure
relief valve during the heating cycle.
The same procedure can be used for both the boost
immersion and immersion backup heater.
Re-Commissioning
Check all electrical and plumbing connections are
secure. Close the drain valve. DO NOT switch on
the immersion heater or Heat Pump while the unit
is empty. With a hot tap open, turn on the cold water
supply and allow unit to refill. When water flows from
the hot tap allow to continue for a short while to purge
air and flush through any disturbed particles. Close
hot tap and then open successive hot taps in system
to purge any air. When completely full and purged
check system for leaks. Replace and secure immersion
heater housing cover. The heating source (immersion
heater or heat pump) can then be switched on.
Expansion Vessel Charge Pressure
Remove the dust cap on top of the vessel. Check the
charge pressure using a tyre pressure gauge. The
pressure (system de-pressured) should be equal to
or slightly above the incoming mains water pressure,
no higher than 0.05 KPa (0.5 bar) above. If it is lower
than the required setting it should be re-charged
using a tyre pump (Schrader valve type). DO NOT
OVER-CHARGE. Re-check the pressure and when
correct replace the dust cap.
15
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