Installation; Important Remarks; Domestic Hot Water; Sealed Systems - Worcester benchmark ZWB 7-25 R 25 HE Design, Installation And Servicing Instructions

Installation

3 Installation
B Always turn off the gas cock before car-
rying out any work on components
which carry gas.
Fixing of the appliance, gas and flue con-
i
nections, commissioning of the system
and electrical connections may only be
carried out by competent persons author-
ised by CORGI.
3.1

Important remarks

B Appliance should only be installed in sealed central
heating systems.
B To avoid gas formation in the system, galvanised radi-
ators or pipes must not be used.
B If a room thermostat is used: do not fit a thermostatic
radiator valve on the radiator in the primary room.
B Add a suitable anti-freeze fluid compatible with alu-
minium to the water in the central heating system.
Suitable products are available from Betz-Dearborn
Tel.: 0151 4209563 and Fernox Tel.: 01799
550811.
B In our experience, the addition of sealing agents to
the water in the central heating system can cause
problems (deposits in the heat exchanger). For that
reason we advise against their use.
3.2

Domestic hot water

Any regulations specified by the local water company
must be observed.
The final 600 mm of the mains cold water connection to
the appliance should be made in copper tube only.
The appliance is suitable for a mains supply having a
maximum pressure of 10 bar. A pressure reducing valve
must be fitted, if necessary.
The hot water outlet temperature is set to be capable of
achieving a maximum of 60°C. The maximum tempera-
ture and the frequency of the recharge of the heat store
may be reset.
Fig. 5
3.3

Sealed systems

The appliance must not be operated without the system
being full of water, properly vented and pressurised.
12
A water flow rate of 11.7 l/min will give a temperature
rise of 40°C. If a higher rise is required then the flow
must be reduced at the tap and the discharge tempera-
ture will rise up to the maximum set figure.
The temperature rise, up to the maximum set by the
user, is automatically maintained by the modulation of
the heat input. In winter, when the mains temperature is
very low, the water flow, adjusted at the tap or shower,
should be reduced to maintain the required delivery
temperature.
It is suggested that long pipe runs to taps or showers
be insulated to prevent the rapid cooling of the water.
All types of single lever mixer taps and thermostatic
mixer units suitable for a mains pressure of up to 10 bar
can be used.
The head of a loose-head shower must not be allowed
to fall within 25 mm of the top the bath to prevent the
risk of water being drawn back into the mains. Alterna-
tively the shower must be fitted with an anti-syphonage
device at the point of the flexible hose connections.
Over-rim bidets may be connected to the appliance pro-
vided that it is in accordance with the requirements of
the local water company. The outlet(s) should be
shrouded and unable to have any temporary hand held
spray attached. No anti-syphonage arrangements are
necessary.
In exceptionally hard water areas a device to prevent
scale formation may be fitted or, alternatively, the maxi-
mum temperature reset to about 45°C which may
reduce the risk of scale formation. The installation of a
scale inhibitor assembly should be in accordance with
the requirements of the local water company. Artificially
softened water must not be used to fill the central heat-
ing system. An isolating valve should be fitted to allow
for servicing.
Devices, such as water meters or back-flow pre-
vention valves, capable of preventing the flow of
expansion water must not be fitted unless sepa-
rate arrangements have been made.
A Zilmet Z160 expansion vessel is the preferred type. A
thread sealant compatible with potable water must be
used. The vessel should be connected into the cold
water mains inlet pipe as close as possible to the appli-
ance.
The expansion vessel has a volume of 10 litres and is
charged to a pressure of 0.75 bar.
6 720 611 441 GB (03.11)