Page 441 - 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

● Motorised valve failure: this is a common occurrence with fully pumped
systems. The valve should be tested to confirm whether it is the valve itself
that has failed or just the motor in the actuator head.
● Boiler failure: this is a more serious fault that may mean specialist diagnosis
and repair by an experienced plumber.
● Airlocks: these can usually be traced to long horizontal runs in the cold feed
to the cylinder as it leaves the cistern. The closer the horizontal run is to the
cistern, the less head of pressure there is on the cold feed. This can create
an airlock before the cold feed drops vertically to the cylinder. Low-pressure
systems always work better when the pipework exits the roof space quickly.
Long horizontal runs create problems with flow rate when the head of
pressure is low.
● The cold feed has a backfall towards the cistern: air collects in the high
point in the pipework. The pipework leaving the cistern should fall away from
the cistern to ensure a good flow rate.
● Noise in the system: this can be due to oscillation of the float-operated
valve. This may be because of a faulty float-operated valve or a missing
cistern wall-strengthening plate, which prevents the cistern wall from
vibrating. Vibration may also come from the immersion heater when the
electricity is turned on. The heater element vibrates quickly, making a
humming sound. The only action here is to replace the heater.
● Overheating of the water: this causes the water to boil and is a problem
found in some older direct systems with a coal-fired back boiler.
● Expansion of the pipework: this causes ticking and creaking noises when
not enough room has been allowed for expansion of the pipework. On new
properties, this type of noise is not allowed and must be traced and rectified.
● Excessively hot water: this is usually caused by immersion heater
thermostat failure. This will need testing and replacing with a thermostat
that has a high limit stat cut-out.
● Uncontrolled heat from a solid fuel appliance: this may occur in direct
systems.
● Cylinder collapse: due to the creation of a vacuum in the cylinder caused by
the hot water dropping as soon as it leaves the cylinder before it enters the
vent pipe; having no vent pipe installed; a blocked vent pipe; or an isolation
valve installed on the vent pipe which is turned off.

SUMMARY

The choice of hot water system is a confusing task. There are so many
systems to choose from, and each one has its advantages and disadvantages.
In this chapter, we have investigated a sample of the most popular systems
from simple point-of-use heaters to Building Regulations-compliant storage
and non-storage systems for whole-house hot water distribution for a variety
of property types and sizes. These systems should be considered carefully to
give the best possible combination of initial cost, efficiency, hot water control,
maintenance costs and eventual replacement.
Hot water is a necessity. How we deliver it is a matter of choice.

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