15
6.0 System Details
© Baxi Heating UK Ltd 2017
Fig. 7
Boiler
Other Tap
Outlets
Expansion
Vessel*
To Hot
Taps
Check
Valve*
Pressure Reducer
Valve*
Stop Tap
*See 6.8 for instances when
these items may be required
IMPORTANT: Where Low Flow Taps or
Fittings are intended to be used in the DHW
system connected to a Baxi 124/128 Combi it is
strongly recommended that the DHW flow rate
DOES NOT fall below 2.5l/min. This will ensure
reliable operation of the DHW function.
6.8 Domestic Hot Water Circuit (Fig. 7)
1. All DHW circuits, connections, fittings, etc. should be fully in
accordance with relevant standards and water supply regulations.
2. Your attention is drawn to:
for GB: Guidance G17 to G24 and recommendation R17 to R24
of the Water Regulations Guide.
for IE: the current edition of I.S. 813 “Domestic Gas Installations”.
3. The Water Regulations recommendations for England and
Wales prohibits backflow from appliances into the wholesome
water supply due to thermal expansion. However this type of
instantaneous combination boiler, with less than 15 litres of
stored capacity, does not require any backflow prevention device
as any thermal expansion is accommodated within the appliance.
It is possible in certain circumstances that other cold water
demands (e.g. washing machines, flushing of W.C.s) may affect
the DHW function of the boiler. In these instances the fitting of a
backflow prevention device and expansion vessel is
recommended.
4. In instances where the mains water supply incorporates a non-
return backflow prevention device, or any other device that
includes one*, it is possible for a build-up of pressure to occur.
This may result in damage to the boiler and other appliances. To
prevent damage to the boiler it is strongly recommended that a
suitable mini expansion vessel is fitted on the mains water inlet
between the boiler and the non-return device. *(The
manufacturer of the device should be consulted if there is any
doubt regarding the presence of a non-return feature).
Even in circumstances where a non-return device is not fitted
any future modifications to the mains inlet (e.g. fitting of a water
meter) should be considered and an expansion vessel fitted. Baxi
cannot accept any responsibility for damage to the boiler if these
recommendations are not followed.
5. The boiler’s maximum working mains pressure is 8 bar,
therefore all pipework, connections, fittings, etc. should be
suitable for pressures in excess of 8 bar. A pressure reducing
valve must be fitted for pressures in excess of 8 bar. The
manufacturer of any outlet fittings, such as a shower valve, may
require a lower maximum pressure. The pressure reduction must
take account of all fittings connected to the DHW system.
6.9 Showers
1. If a shower control is supplied from the appliance it should be
of the thermostatic or pressure balanced type. Thermostatic type
shower valves provide the best comfort and guard against water
at too high a temperature. Existing controls may not be suitable -
refer to the shower valve manufacturer.
6.10 Hard Water Areas
1. Only water that has NOT been artificially softened must used
when filling or re-pressurising the primary system. If the mains
cold water to the property is fitted with an artificial
softening/treatment device the source use to fill or
re-pressurise the system must be upstream of such a device.
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