Important
In instances where the mains water supply incorporates a non-re
turn backflow prevention device, or any other device that includes
one*, it is possible for a build-up of pressure to occur. This may re
sult 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. Main cannot
accept any responsibility for damage to the boiler if these
recommendations are not followed.
The boiler’s maximum working mains pressure is 8 bar, therefore all pipe
work, 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.
5 Before installation
38
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 pre
vention device as any thermal expansion is accommodated within the ap
pliance. It is possible in certain circumstances that other cold water de
mands (e.g. washing machines, flushing of WCs) may affect the DHW
function of the boiler. In these instances the fitting of a backflow prevention
device and expansion vessel is recommended.
