14
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.
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 23 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.
IMMERSION REMOVAL
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
backnut(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.
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 10°C to 70°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.