Page 440 - 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

● The hot water appliance: this should be serviced annually in line with the
manufacturer’s instructions.
l The cistern (for open vented systems): cisterns should be checked periodically
for sediment build-up on the bottom of the cistern. If a cistern is to be replaced,
then the replacement cistern should be pre-assembled before decommissioning
the system. This will reduce the length of decommissioning time.
● Taps and terminal fittings such as float-operated valves: taps should be
re-washered and float-operated valves checked for correct shut-off, and
water levels checked and adjusted as necessary.
l Isolation valves such as full-way gate valves and service valves: these
should be checked to ensure that they shut off the flow of water fully.
l Thermostats: systems, such as immersion heaters and boilers, should
be run to operating temperature to ensure the correct operation of any
thermostats. They should be checked using digital thermometers.
● Shower mixing valves and pumps: these should be inspected to
ensure that they are functioning in accordance with the manufacturer’s
specifications. Flow rates can be confirmed by using a weir cup. Filters
can be removed and cleaned. The operation of the flow switch on shower
boosting pumps should be checked, as these turn the shower pump
on. Showerheads should be cleaned of any scale build-up as this can
significantly reduce the flow of water.

7 REPLACE DEFECTIVE

COMPONENTS

The replacement of float-operated valves, taps, pumps and valves is covered in
Chapter 5, Cold water systems.

Faults with open-vented hot water systems

There are many faults that can occur with open-vented hot water systems.
Some of these may be due to poor system design but most occur with use.
Some of the more common faults are:

● Loss of hot water: this may be due to evaporation of the water in the feed
and expansion (F&E) cistern installed on double-feed indirect cylinders, with
gravity circulation to the heat exchanger. This is usually due to a sticking
float-operated valve (FOV) that fails to top the water up as evaporation
occurs. Because the FOV is stuck in the off position, the water evaporates
down to the primary flow pipe and this stops circulation to the heat
exchanger and prevents the cylinder getting hot. To rectify the fault, the FOV
in the F&E cistern should be removed and repaired/replaced.
● Immersion heater element failure: this is usually due to corrosion of the
immersion heater element sheath, allowing water to penetrate the heater
element. This causes a short circuit, which usually blows the fuse. The
immersion heater will need to be replaced.
● Cylinder thermostat failure: a very rare fault. The thermostat should first
be tested to confirm that it has failed before replacing it.

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