Page 525 - 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 7 Central heating systems

Tasks that may require system drain down

There are many situations where draining of the system is needed, such as:

l replacing the hot water storage cylinder
l boiler replacement
l decommissioning of components such as radiators; here, the radiator,
brackets and pipework should be removed and the pipes capped off at the
branch to the flow and return pipes
l replacement of motorised valves
l cutting into an existing system to alter or extend it; drain down should be
conducted when all other installation work has been carried out
l power flushing.
Power flushing a system

During the last task we looked at, it may become apparent that the system
contains a lot of black water and even sludge. If this is the case, the system may
be in need of a power flush. When replacing boilers, a power flush is required to
remove any sludge within the system as part of the warranty. Manufacturers’
warranties are void if this is not carried out.
Power flushing involves using a special high-powered pump to circulate
cleaning chemicals and de-sludging agents through the system. These powerful
chemicals strip the old corrosion residue from the system, ensuring that the
system does not contain sediment that may be harmful to new boilers, controls
and valves.

Once the power flushing is complete, the system may have an inhibitor added
to the system water to keep the system free from corrosion.

Routine maintenance tasks
Routine maintenance should be conducted on a 12-monthly basis. Routine
maintenance includes:
l checking the pressure charge in expansion vessels on sealed systems, system
boilers and combination boilers
l checking the operation of pressure relief valves on sealed systems, system
boilers and combination boilers
l checking and topping up (if required) the pressure on system boilers and
combination boilers
l visually checking for any signs of leakage on pipework, controls and appliances
l boiler servicing
l checking the correct operation of thermostats, motorised valves and
thermostatic radiator valves
l checking the water level in F and E cisterns, and adjusting as necessary
l ensuring that the system is reaching full temperature.

Dealing with simple system faults
It is impossible to cover all scenarios when dealing with system faults. Often,
the reason for a fault developing is clear and stems from poor design when the

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