Page 454 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

The C-plan plus (two-pipe) system

This is a two-pipe system that is basically an updated version of the C-plan
system and incorporates full thermostatic control of both heating and hot
water circuits. Room temperatures are controlled by a room thermostat and
thermostatic radiator valves, while the hot water temperature is controlled by a
cylinder thermostat linked to a single two-port motorised zone valve installed
on the gravity flow before it enters the heat exchanger at the hot water storage
cylinder.
The C-plan plus system is accepted as Building Regulations Document
L1b compliant for the updating of existing systems. Some advantages and
disadvantages of the C-plan plus system are listed in Table 7.3.
 Table 7.3 Advantages and disadvantages of the C-plan plus system
Advantages Disadvantages
All of the heat emitters reach the same The system is not as controllable as more
temperature modern fully pumped systems
Condensing-type boilers cannot be fitted to
The two-pipe system is much quicker at
heating up than the one-pipe system; this this type of installation because of the gravity
saves on fuel usage circulation needed by the hot water storage
cylinder
The system is Building Regulations The boilers fitted to this type of system are
Document L compliant only about 78% efficient or less
Full control over both heating and hot water
circuits is possible

The C-plan plus (two-pipe) semi-gravity system has total thermostatic control with
the inclusion of a room thermostat and a cylinder thermostat linked to a single
two-port motorised zone valve on the gravity flow before it enters the heat exchanger
on the storage cylinder; the system must include controls to prevent boiler cycling.
Motorised valve
Cylinder Room
thermostat thermostat
15 mm cold feed pipe

Wiring
centre

Programmer

28 mm
gravity
primaries Pump
Boiler

p Figure 7.5 C-plan plus system

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