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4.0
4.2 cENTrAL HEATING cIrcuIT & SYSTEM
a)
central heating system
The Gledhill GB35C combination boiler is suitable for fully pumped sealed systems
only. The sealed heating system is shown schematically in figure 4.1. The sealed
system installation must comply with the appropriate requirements of current
issues of BS5449, BS6759, BS6798 and BS7074.
A draining tap or taps conforming to the current issue of BS 879, must be
provided at all the low points of the system to allow the entire central heating
system to be drained.
It is recommended that manual air vents are provided at all the high points of
the system.
The minimum initial (cold) system and expansion vessel pressure must be at least
0.5 bar greater than h/10 (see figure 4.1). For example if height of the system high
point above the boiler is 7m, then the minimum charge pressure should be greater
than 1. bar (7/10 + 0.5 = 1. bar). This will minimise the chances of the system
entraining air and/or 'kettleing' noises from the boiler during operation.
b)
Treatment of water in the heating system
All central heating systems will be subject to corrosion unless an appropriate
water treatment is applied. This will deteriorate the efficiency of the system as the
corrosion sludge accumulates within the system risking damage to equipment
such as the pump, valves and boiler. It will also give rise to boiler noise and
circulation problems. The system commissioning, cleansing and dosing must
comply with BS7593 requirements.
When upgrading existing systems it is necessary that the system is cleaned prior
to treatment in order to remove any sludge and reduce the likelihood of these
deposits damaging the new components.
When fitting new systems flux may be present within the system, which can lead
to damage of system components.
All systems must be thoroughly drained and flushed out. The recommended
flushing and cleansing agents are Betz-Dearbon Sentinel X300 or X400 and
Fernox Superfloc Universal Cleanser which should be used in accordance with
the manufacturer's instructions.
The only system additives recommended are Betz-Dearbon Sentinel X100 and
Fernox-Copal and these should be used following the inhibitor manufacturer's
instructions. It is important to check that the inhibitor concentration after
installation, system modification and at every service is in accordance with the
manufacturer's instructions.
Important Notes:-
•
Failure to flush and add inhibitor correctly to the system at the correct
concentration recommended in the manufacturers instructions will
invalidate the appliance warranty.
•
Failure to fit a suitable system filler in existing systems will also invalidate
the appliance warranty.
•
In the case of an existing installation, the system MUST be thoroughly flushed
before installing the new boiler. Power flushing is the recommended option
for existing installations because all high efficiency boilers have smaller
waterways than traditional boilers. A suitable system filter (e.g. Spirovent
SV3-05-T) fitted in the boiler return is STRONGLY recommended in new
systems and must be fitted in existing systems.
•
It is imperative when draining down to the primary boiler circuit that any
heating circuit debris is not drawn into the boiler waterways. Before refilling,
the system filter should be cleaned
SYSTEM DESIGN AND PLANNING INFOrMATION
c)
System bypass
The boiler is fitted with an integral bypass valve for
the central heating circuit as shown in figure 4.. The
bypass should be adjusted so that when the boiler is in
the central heating mode, the temperature difference
across the boiler is between 11 and 0ºC. The boiler
flow and return temperature can be measured using
the digital display of the boiler.
When adjusting the bypass valve, it is important
to ensure that the central heating circuit flow rate
is sufficient to heat all the radiators uniformly and
simultaneously.
Figure 4.2
Bypass Adjuster
d)
System controls
A 4 hour electro-mechanical programmer is supplied
fitted to the boiler. Further external controls e.g. room
thermostat and thermostatic radiator valves should
be fitted to comply with the relevant requirements
of Part L1 of the Building Regulations. For further
information see: -
•
The current issues of Approved Documents L1A
& L1B
•
The Domestic Heating Compliance Guide
•
GIL 59, 000 : Central heating system specification
(CheSS)
•
GPG 30, 001: Controls for domestic central
heating system and hot water. BRECSU.
Page 15
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