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 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 20 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 hose-
pipe 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 valve to drain the cylinder.
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.
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°C to 72°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
Switch OFF electrical supply to the immersion
heater before removing the cover.
Open the cover
to the immersion heater housing and disconnect
wiring from immersion heater. Carefully remove the
thermostat capillaries. 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 68).
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. Replace thermostat capillaries into pockets.
Connect wiring to element. Check, and close and
secure immersion heater housing cover.
Re-Commissioning
Check all electrical and plumbing connections are
secure. Close the drain cock.
DO NOT switch on the
immersion heater 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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