Page 450 - 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

Wet central
heating
systems

Open vented Sealed
(low pressure) (pressurised)
systems systems

Gravity hot Fully pumped System boiler
water/pumped Pumped
heating systems heating only systems systems
systems

Systems using
One-pipe Two-pipe Y-plan S-plan external
systems systems system system expansion
vessel

Microbore
systems Combination
C-plan boiler
system
systems

C-plan plus
system
p Figure 7.1 The development of pumped central heating

Low pressure, open vented central heating systems

Pumped central heating only systems
The simplest of all heating systems – pumped central heating only systems – do
not contain any provision for heating the domestic hot water. They serve only
the heat emitters, usually radiators/convectors, for domestic installations. The
cold feed and the vent pipe can either be taken direct from the boiler or direct
from the heating pipework. They are generally two-pipe systems, with the
central heating circulating pump installed on the flow pipe.

Semi-gravity heating systems
Semi-gravity heating systems utilise gravity circulation to heat the domestic
secondary water and pumped central heating circulation. The heat exchanger
within the hot water storage cylinder is connected to the boiler by the primary
flow and return pipes, usually 28 mm in diameter with a 22 mm vent pipe branched
from the primary flow and a 15 mm cold feed pipe connected to the primary
return. They may still be found as existing systems in older properties.

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