gledhill GB10 Installation And Servicing Instructions page 13

discharge in a conspicuous external position. It should not have any other pipework directly branched
into it.
(g) The water level in the F & E cistern should be at least 250mm above the highest point on the system
including the radiators
3.5.2. Sealed heating system
(a) Design Standards
The sealed heating system is shown schematically in diagram 3.4. The sealed system installation must
comply with the appropriate requirements of current issues of BS5449, BS6759, BS6798 and BS7074.
(b) Safety Valve
A non-adjustable safety valve must be fitted to a sealed system. It shall be pre-set with a lift pressure of
3 bar and incorporate a seating of resilient material, a test device and a connection to the drain.
(c) Safety Valve Drain
The drain from a safety valve must be routed outside the building and positioned so that any discharge
can be seen. It must not discharge above an entrance or window or any type of public area and be clear
of any electrical fittings.
(d) Pressure Gauge
A pressure gauge with a set pointer and covering at least 0 – 4 bar shall be fitted permanently to the
sealed system. It should be positioned where it can be seen when filling the system.
(e) Expansion Vessel
A diaphragm type expansion vessel, conforming to the current issue of BS4814 (See also BS7074
Parts 1 and 2) must be connected to the inlet side of the circulating pump (see diagram 3.4) unless laid
down differently by the manufacturer.
The water content of the boiler is given in table 3.1.
The expansion vessel volume depends on the total water volume of the system and the initial system
design pressure as shown below in table 3.3. For any system an accurate calculation of vessel size is
given in the current issue of BS5449 and BS7074 Part 1. For example; A higher initial design charge
pressure requires a larger volume vessel.
The initial vessel charge pressure must not be less than the static head of the system, that is the height
of the highest point of the system above the expansion vessel.
VER: 02.3 _260505
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