3
G3 Requirements (extracts taken from G3 regulations)
(2)
A hot water system, including any cistern or other vessel that supplies water to or receives expansion water from
a hot water system, shall be designed, constructed and installed so as to resist the effects temperature and pressure
that may occur either in normal use or in the event of such malfunctions as may reasonably be anticipated, and must be
adequately supported.
(3)
A hot water system that has a hot water storage vessel shall incorporate precautions to:
(a)
prevent the temperature of the water stored in the vessel at any time exceeding 100°C: and
(b)
ensure that any discharge from safety devices is safely conveyed to where it is visible but will not
cause a danger to persons in or about the building.
In the Secretary of State’s view Requirement G3(3) will be met for a
hot water storage system
that has a vented storage
vessel if:
a.
the storage vessel has a suitable vent pipe connecting the top of the vessel to a point open to the atmosphere
above the level of the water in the cold water storage cistern and over it; and,
b.
in addition to any thermostat, either the heat source, or the storage vessel is fitted with a device that will
prevent the temperature of the stored water at any time exceeding 100°C; and,
c.
the hot water system has pipework that incorporates a provision for the discharge of hot water from the safety
devices to an appropriate place open to atmosphere where it will cause no danger to persons in or about
the building.
Vented hot water storage systems
3.12
Vented
hot water storage systems
should incorporate a vent pipe of an adequate size, but not less than 19mm
internal diameter, connecting the top of the hot water storage vessel to a point opne to the atmosphere obove and over
the level of the water in the cold water storage sytem.
3.13
In addition to the vent pipe referred to in 3.12 and any thermostat provided to control the temperature of the
stored water to a desired temperature, vented
hot water storage systems
should incorporate either:
a.
for all direct heated sources, a non-self-resetting energy cut-out to disconnect the supply of heat to the storage
vessel in the event of the storage system overheating: and,
for all indirect heat sources, an overheat cut-out to disconnect the supply of heat to the storage vessel in the
event of the stored water overheating so that the temperature of the stored water does not exceed 100°C.
3.14
Vent pipes should discharge over a cold water storage cistern conforming to BS 417-2:1987. Specification for
galvanized low carbon steel cisterns, cistern lids, tanks and cylinders. Metric units; or BS 4213:2004 Cisterns for domestic
use. Cold water storage and combined feed and expansion (thermoplastic) cisterns up to 500 litres. Specification; as
appropriate.
3.15
The cold water storage cistern into which the vent pipe discharges should be supported on a flat, level, rigid
platform which is capable of safely withstanding the weight of the cistern when filled with water to the rim and fully
supporting the bottom of the cistern over the whole of its area. The platform should extend a minimum of 150mm in all
directions beyond the edge of the maximum of the cistern.
Note: When an existing metal cistern is replaced, or a plastic cistern is replaced by one with larger dimensions, the
existing support should be upgraded, as necessary, with one in accordance the paragraph 3.15.
3.16
The cistern should be accessible for maintenance, cleaning and replacement.
