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 21 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
Before removing the immersion heater the unit must be
drained.
Before draining ensure the water, electrical
supply and boiler are OFF.
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.
Remove the cover to 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
terminal shroud. Unscrew immersion heater backnut
and remove immersion heater from the unit. A key
spanner is supplied with the cylinder unit for easy
removal/tightening of the immersion heater.
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.
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 70 351 65).
Replace immersion heater ensuring the (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 the terminal shroud. Connect
wiring to element. Check, and close and secure
immersion heater housing cover.
Expansion Vessel Charge Pressure
While system is de-pressurised check 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.
DO NOT switch on
the immersion heater(s) or boiler 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 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. Replace and secure immersion heater housing
cover. The heating source (immersion heater or boiler)
can then be switched on.
Maintenance
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