Page 519 - 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 7 Central heating systems

l Underfloor heating: connecting extra pipework loops to an existing
underfloor system is possible only if the manifold is replaced, allowing
connection of the new circuit. The heat source/boiler and the circulating pump
should be checked to ensure that they can cope with the extra heat load.

Soundness test requirements for pipework

Most domestic systems use three types of pipe materials:
1 Copper tubes and fittings: grades R220 and R250 are generally used for
domestic central heating installations. Grade R250 in sizes 15 mm, 22 mm
and 28 mm are used for minibore installations, while R220 is used for
microbore systems, usually 10 mm.
2 Low carbon steel pipes and fittings: very rarely used for domestic
installations but used extensively on commercial and industrial systems. KEY POINT
3 Polybutylene pipes and fittings: fast becoming the material of choice Testing of pipework, both
for new-build installations because of its ease of installation. It should be metallic and plastic, is
covered in Chapter 5,
remembered, however, that the connections to any heat-producing appliances Cold water systems.
must be made using copper for the first metre away from the appliance.

Installing and testing components

Types of information to be referred to for installation work:
l manufacturer instructions should always be read before any installation
takes place
l specification drawings should be followed wherever possible; alterations to
the original drawings should be done with care
l verbal instructions from the customer must be considered.

The installation of tubes and fittings has been covered extensively in earlier
chapters of this book, but central heating systems demand careful consideration
because of the temperature that the systems run at. With water at 80°C for the
flow and 60°C for the return, the pipework, regardless of the material used, will
expand and contract as the pipe heats up and cools down. Obviously, not all
of the materials expand at the same rate, but provision should be made at the
installation stage to allow for expansion and contraction if problems with noise
are to be avoided. Here are some points to consider:
l Polybutylene pipe expands more than copper tube, but copper is much more
rigid than polybutylene. When installing pipes in wooden floors, enough
room should be allowed in any notches made. If the pipes are too tight in the
joist, they will ‘tick’ as they expand and contract. This is very pronounced
with central heating systems installed using copper tubes because the water
reaches a higher temperature.
l Clipping and securing pipework becomes very important. The clipping
distances for the various pipes and tubes we use are known from previous
learning, but become critical where polybutylene pipe is concerned,
especially when used with central heating installations, because as the pipe
becomes hot, it starts to soften and this leads to the pipe ‘drooping’ between
joists and between clips. This not only looks unsightly but can put excess
strain on the joints.
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