Mira Realm Installation, Operation, Maintenance Manual page 8

2.1. Instantaneous gas-heated showers (e.g. combination boilers) - The
shower MUST be installed with a multipoint gas water heater or combination
boiler of a fully modulating design (i.e. where the water draw-off rate indirectly
controls the gas flow rate to the burner).
A drop tight pressure reducing valve (PRV) MUST be fitted if the supply
pressures exceed 3 bar maintained.
An expansion vessel MUST be fitted (and regularly maintained) if any form of
backflow prevention device is fitted, e.g. non-return valve, PRV. This will ensure
that excess expansion or pulse pressures do not damage the product or the
plumbing system. The expansion vessel may already be fitted within the boiler
(check with the manufacturer) and is in addition to the normally larger central
heating expansion vessel.
The layout and sizing of pipework MUST be such that nominally equal inlet
supply pressures are achieved AND the effects of other draw-offs are
minimized.
The hot supply temperature MUST be at least 10 °C hotter than the required
blend temperature for optimum performance.
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