Page 371 - 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

The primary flow and return pipes to and from the boiler/circulator should be
a minimum of 28 mm regardless of pipe length, unless stated differently in the
manufacturer’s instructions.

22 mm vent pipe discharging into the 22 mm vent pipe discharging into the
CWSC and sealed with a grommet CWSC and sealed with a grommet

22 mm or 28 mm cold feed to
22 mm or 28 mm full-way secondary hot water system
gate valve or lever type 22 mm or 28 mm full-way gate valve
spherical ball valve
or lever-type spherical ball valve
22 mm draw-off to the bath then reduced 22 mm draw-off to the bath then reduced
to 15 mm to all other appliances to 15 mm to all other appliances

Heat source. Top immersion heater for daytime top-up.
Bottom immersion heater heats up all the water in the
22 mm primary cylinder via a daytime controller for the use of cheap
circulating pipes rate overnight electricity
connect the heat
sorce to the cylinder
Heat source. Gas circulator or
back boiler behind a solid fuel fire

p Figure 6.3a The direct system of hot water p Figure 6.3b The direct system of hot water with immersion
heaters
Direct cylinders, when connected to solid fuel back boilers, are susceptible to
boiling because there is no effective method of temperature control.
 Table 6.2 Advantages and disadvantages of direct systems
Advantages Disadvantages
Quick heat up time of the water Risk of rusty water being drawn off at the taps if the wrong
Cheap to install type of boiler is used
High risk of scale build-up in hard water areas if the water
temperature exceeds 65°C
High risk of scalding because of the lack of thermostatic
control

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