Page 502 - 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

There are two levels of controls for domestic properties and these are set out in
Central Heating System Specification (CHeSS) CE51 2008:
1 Good practice: This set of controls achieves good energy efficiency in
line with Approved Document L 2010. This is described in detail in the
CHeSS document:
a HR7 – Good practice for systems with a regular boiler and a
separate hot water store:
i Full programmer
ii Room thermostat
iii Cylinder thermostat

iv Boiler interlock (see note 1)
v TRVs on all radiators, except in rooms with a room thermostat
vi Automatic bypass valve (see note 2).
b HC7 – Good practice for systems using a combination boiler or
Combined Primary Storage Unit boiler:
i Time switch
ii Room thermostat
iii Boiler interlock (see note 1)
iv TRVs on all radiators, except in rooms with a room thermostat
v Automatic bypass valve (see note 2).
2 Best practice: This standard uses enhanced controls to further enhance
energy efficiency in line with Approved Document L1a/b 2010. This is
described in detail in the CHeSS document:
a HR8 – Best practice for systems with a regular boiler and a separate
hot water store:
i Programmable room thermostat, with additional timing
capability for hot water
ii Cylinder thermostat
iii Boiler interlock (see note 1)
iv TRVs on all radiators, except in rooms with a room thermostat
v Automatic bypass valve (see note 2)
vi More advanced controls, such as weather compensation, may be
considered.
b HC8 – Best practice for systems using a combination boiler or
Combined Primary Storage Unit:
i Programmable room thermostat
ii Boiler interlock
iii TRVs on all radiators, except in rooms with a room thermostat
iv Automatic bypass valve (see note 2)
v More advanced controls, such as weather compensation, may be
considered.
Note 1 (from CHeSS): Boiler interlock is not a physical device but an
arrangement of the system controls (room thermostats, programmable
room thermostats, cylinder thermostats, programmers and time switches)
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