Page 387 - 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

Direct unvented under-sink storage heaters
Unvented under-sink hot water storage heaters are connected direct to the mains cold
water supply and deliver hot water at near mains cold water pressure. Because they
have less than 15 litres of storage, they are not subject to the stringent regulations
that surround the installation of larger unvented hot water storage units.
The expansion of water may be taken up within the pipework, provided
the pipework is of sufficient size to cope with the water expansion. If not,
then an external expansion vessel will be required.

Expansion vessel Single check valve
Expansion relief valve Isolation valve
Pressure reducing
valve
15 litre point-of-use unvented Tundish Stop valve
hot water storage heater
Discharge pipe

p Figure 6.19 Direct-type under-sink type unvented hot water storage cylinder with external
expansion vessel

p Figure 6.20 Unvented-type under-sink storage water heater with expansion vessel

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