Page 437 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 6 Hot water systems

be a source of frustration within systems running at high pressures because
of the noise it can generate. Incorrect clipping distances and, often, lack of
clips and supports can put a strain on the fittings and cause the pipework
to reverberate throughout the installation, even causing fitting failure and
leakage. To prevent these occurrences, the installation should be checked as
it progresses and any deficiencies brought to the attention of the installing
engineer. Upon completion, the system should be visually checked before
flushing and commissioning begins.
● Leakage: water causes a huge amount of damage to a building and can
even compromise the building structure. Leakage from pipework, if left
undetected, causes damp, mould growth and an unhealthy atmosphere. It
is, therefore, important that leakage is detected and cured at a very early
stage in the system’s life. It is almost impossible to ensure that every joint
on every system installed is leak free. Manufacturing defects on fittings and
equipment, as well as damage, sometimes cause leaks. Leakage due to badly
jointed fittings and poor installation practice are much more common,
especially on large systems where literally thousands of joints have to be
made until the system is complete. These can often be avoided by taking p Figure 6.63 A plumber’s nightmare!
care when jointing tubes and fittings, using recognised jointing materials A badly designed plumbing system
and compounds, and following manufacturers’ recommended jointing makes fault finding almost
techniques. impossible

The risk from Legionella pneumophila in hot water systems
According to the HSE, instances of Legionnaires’ disease derived from hot
water supply have diminished over recent years due to better installation
techniques and greater awareness of sterilisation methods. However, large hot
water systems can often be complex in their design and, therefore, still present
a significant risk of exposure. The environments where Legionella bacteria
proliferate are listed below.

● At the base of the cylinder or storage vessel where the cold feed enters
and cold water mixes with the hot water within the vessel. The base of the
storage vessel may well eventually contain sediments, which support the
bacterial growth of Legionella.
● The water held in a secondary circulation system between the outlet and the
branch to the secondary circulation system, as this may not be subject to
the high temperature sterilisation process.

In general, hot water systems should be designed to aid safe operation by
preventing or controlling conditions that allow the growth of Legionella. They
should, however, permit easy access for cleaning and disinfection. The following
points should be considered.
● Materials such as natural rubber, hemp, linseed oil-based jointing compounds
and fibre washers should not be used in domestic water systems. Materials
and fittings acceptable for use in water systems are listed in the directory
published by the Water Research Centre.
● Low-corrosion materials (copper, plastic, stainless steel, etc.) should be used
where possible.

425

9781510416482.indb 425 29/03/19 9:02 PM