Page 473 - 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

Modern condensing boilers are around 94 per cent efficient, releasing only
6 per cent of wasted heat in the cooler flue gases to the atmosphere. Some
advantages and disadvantages of condensing boilers are listed in Table 7.12.

 Table 7.12 Advantages and disadvantages of condensing boilers
Advantages Disadvantages
Building Regulations Document L compliant High maintenance compared with other
Very high efficiency boilers
Sealed (pressurised) system gives better Siting of the condense pipework can often
heating flow rates prove difficult
System corrosion can be reduced Does not work if the condense line freezes
during cold weather
Very quiet in operation
Use more gas when not in condensing mode
Can be used with all modern fully pumped
heating systems (system boilers)
No F and E cistern required in the roof space
Very good flow rate on hot water supply
(condensing combination boilers)

The types of boiler that can be used with wet central heating systems fall into
three distinct categories:
1 system boilers
2 traditional boilers
3 combination boilers.

System boilers
A system boiler is an appliance where all necessary safety and operational
controls are included and fitted directly to the boiler. There is no need for a
separate expansion vessel, pressure relief valve or filling loop, and this makes the
installation much simpler.

Traditional boilers
A traditional boiler does not contain any form of expansion vessel or operational
controls, such as the pump or filling loop. It is, however, a condensing boiler.

Combination boilers
In recent years, combination boilers have become one of the most popular
forms of central heating in the UK. A combination boiler provides central
heating and instantaneous hot water supply from a single appliance. Modern
combination boilers are very efficient and contain all the safety controls
(i.e. expansion vessel, pressure relief valve) of a sealed system. Most ‘combis’
also have an integral filling loop.

Oil-fired central heating appliances

Oil-fired boilers use two different firing methods:
1 pressure jets or atomising burners
2 vapourising burners.

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