Page 435 - 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

be used immediately, as there is a very real risk that the water within the system
could become stagnant. In practice, it is almost impossible to affect a complete
drain down of a system, particularly large systems, where long horizontal
pipe runs may hold water. This, in itself, is very detrimental as corrosion can
often set in and this can also cause problems with water contamination. It is
recommended therefore that, to minimise the risk of corrosion and water quality
problems, systems should be left completely full and flushed through at regular
intervals of no less than twice weekly, by opening all terminal fittings until the
system has been taken permanently into operation. If this is the case, then
provision for frost protection must be made.

Taking flow rate and pressure readings
Once the hot water system has been filled and flushed, the heat source
should be put into operation and the system run to its operating temperature.
Thermostats and high-limit thermostats should be checked to ensure that they
are operating at their correct temperatures. When the system has reached full
operating temperature and the thermostats have switched off, the flow rates,
pressures and water temperatures can then be checked against the specification
and the manufacturer’s instructions. This can be completed in several ways:
● Flow rates can be checked using a weir gauge. This is sometimes known as
a weir cup or a weir jug. The method of use is simple. The gauge has a slot
running vertically down the side of the vessel, which is marked with various
flow rates. When the gauge is held under running water, the water escapes
out of the slot. The height that the water achieves before escaping from the
slot determines the flow rate. Although the gauge is accurate, excessive flow
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rates will cause a false reading because the water will evacuate out of the p igure 6.61 Checking hot water
top of the gauge rather than the side slot. flow rates
● System pressures (static) can be checked using a Bourdon pressure gauge
at each outlet or terminal fitting. Bourdon pressure gauges can also be
permanently installed either side of a boosting pump to indicate both inlet
and outlet pressures.
l Both pressure (static and running) and flow rate can be checked at outlets
and terminal fittings using a combined pressure and flow rate meter.
● The temperature should be checked using a thermometer at the hot water
draw-off to ensure that it is at least 60°C but does not exceed 65°C. Each
successive hot water outlet, moving away from the storage vessel, should
be temperature checked to ensure that any thermostatic mixing valves are
operating at the correct temperature and that the hot water reaches the
outlet within the 30-second limit. If a secondary return system is installed,
then the circulating pump should be running when the tests are conducted
and the temperature of the return checked just before it re-enters the
cylinder, to ensure that the temperature is no less than 10°C lower than p igure 6.62 Using an infrared
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the draw-off, 50°C minimum. thermometer

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