Technical data
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 25 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 ows 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 tted. 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 sufcient 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 t a new gasket
(part number 95 611 822).
Replace immersion heater(s) ensuring the lower (90° 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 pressure 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 rell. DO NOT switch on the immersion heater(s) or boiler until the unit is full. When water ows
from the hot tap allow to ow for a short while to purge air and ush 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). If necessary the temperature can be adjusted by inserting a at bladed screwdriver in the adjustment knob
on top of the immersion heater thermostat and rotating, (see Fig 8, page 12) for adjustment details. 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.
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