Page 462 - 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

these could indicate a potential component malfunction. The system is usually
pressurised to around 1 bar. There are several types of fully pumped alternatives:

l sealed systems with an external pressure vessel
l system boilers that contain all necessary safety controls
l combination boilers.

All fully pumped systems, such as those with two, or three or more, two-port
zone valves (known as the S-plan and the S-plan plus), or a three-port
mid-position valve (known as the Y-plan) or a three-port diverter valve (known
as the W-plan), can be installed as sealed systems or can be purpose-designed
‘heating only’ systems using a combination boiler with instantaneous hot water
supply. All the pipework layouts described below can be used with the three
boiler systems above.

Fully pumped systems with three or more two-port zone valves
(known as the S-plan plus)
The S-plan plus has three or more two-port motorised zone valves to
control the primary and heating circuits separately by the cylinder and room
thermostats respectively. This system is recommended for dwellings with a
floor area greater than 150 m because it allows the installation of additional
2
two-port zone valves to zone the upstairs heating circuit from the downstairs
circuit. A separate room thermostat, and possibly a second time clock/
programmer, would also be required for upstairs zoning. A system bypass is
required for overheat protection of the boiler.

Upstairs timer switch Upstairs room
System bypass thermostat

Two-port zone Cylinder
valve to hot water thermostat
22 mm flow and
return pipework Two-port
zone valve for
Expansion upstairs circuit
vessel
Downstairs room
thermostat

Two-port
zone valve for
downstairs
circuit

Wiring centre
Programmer
Pressure gauge
Filling loop
Pressure relief valve
and discharge pipework

p Figure 7.18 The sealed S-plan plus system

450

9781510416482.indb 450 29/03/19 9:02 PM