15
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.
Similarly cleaning of the strainer element and
replacement of the air in the expansion vessel 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 document.
INSPECTION
The immersion heater boss can be used as an
access 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 reseats correctly
when released. NOTE: Water discharged may be
very hot!
Repeat the above procedure for the Expansion
Relief Valve.
STRAINER
Turn off the cold water supply, boiler and immersion
heaters. 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 water. Re-assemble ensuring the seal
is correctly fitted. DO NOT use any other type of
sealant.
DESCALING IMMERSION HEATER(S)
Before removing the immersion heater(s) the unit
must be drained. Ensure the water, electrical supply
and boiler are OFF before draining. Attach a
hosepipe to the drain cock having sufficient length
to take water to a suitable discharge point below the
level of the unit. Open a hot tap close to the unit and
open drain cock to drain unit.
DIRECT UNITS
Switch on electrical supply to the immersion
heater(s) and allow to heat up to normal working
temperature (60ºC recommended, approximately
graduation 4 on the thermostat). If necessary the
temperature can be adjusted by inserting a flat
bladed screwdriver in the adjustment knob on top of
the immersion heater thermostat and rotating.
The adjustment range 1 to 5 represents a
temperature range of 12°C to 68°C. Check the
operation of thermostat(s) and that no water
has issued from the expansion relief valve or
temperature/pressure relief valve during the heating
cycle.
INDIRECT UNITS
Open the cover(s) to the immersion heater
housing(s) and disconnect wiring from immersion
heater(s) thermostat(s). Remove thermostat by
carefully pulling outwards. Remove thermostat
capillary sensors from the pockets on the immersion
heater. Unscrew immersion heater backnut(s) and
remove immersion heater from the unit. A key
spanner is supplied with the cylinder unit for easy
removal/tightening of the immersion heater(s). Over
time the immersion heater gasket may become stuck
to the mating surface. To break the seal insert a
round bladed screwdriver into one of the pockets on
the immersion heater and gently lever up and down.
Carefully remove any scale from the surface of the
element(s). DO NOT use a sharp implement as
damage to the element surface could be caused.
Ensure sealing surfaces are clean and seals are
undamaged, if in doubt fit a new gasket
(part number 95 611 822).
Replace immersion heater(s) ensuring the lower
(right angled) element hangs vertically downwards
towards the base of the unit. It may be helpful to
support the immersion heater using a round bladed
screwdriver inserted into one of the thermostat
pockets whilst the backnut is tightened. Replace
thermostat capillaries into pocket. Replace the
immersion heater thermostat by carefully plugging
the two male spade terminations on the underside
of the thermostat head into the corresponding
terminations on the element. Rewire, check, close
and secure immersion heater housing cover(s).
EXPANSION VESSEL CHARGE PRESSURE
Remove the dust cap on top of the vessel. Check
the charge pressure using a tyre pressur
e gauge.
The pressure (with system de-pressurised) should
be 0.35MPa (3.5 bar). 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.
RE-COMMISSIONING
Check all electrical and plumbing connections are
secure. Close the drain cock. With a hot tap open,
turn on the cold water supply and allow unit to
refill. DO NOT switch on the immersion heater(s)
or boiler until the unit is full. When water flows
from the hot tap allow to flow 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. The heating source
(immersion heater(s) or boiler) can then be switched
on.
MAINTENANCE
