Unit 318 L.O 2

Single point heater

What are the components?

Unit 318 Install and
maintain gas water

heating and wet
central heating

appliances

Outcome 2

Know the types of gas water heating and wet central
heating appliances and their layout requirements.

Instantaneous water heater

The major advantage of an instantaneous water heater
is that it heats water directly from the cold mains as it
passes through the appliance. Which means it can
supply hot water instantaneously for any length of
time (5 minutes maximum for a flue-less single-point).
As soon as any of the water points connected to the
appliance are turned on, the burner ignites. It then
heats the cold water as it passes through the heat
exchanger to the hot water outlet, providing hot water
at mains pressures. This method is very economical
because the appliance operates only when hot water
is being demanded.

Open Ended

What type of boilers are there?

Boilers

Boiler types
• Back boiler
• System boiler
• Independent boiler
• Combination boiler
• Electric boiler
• Condensing
• Floor standing
• Wall mounted

Boilers

Boilers
These are covered by Building Regulations part J – heat
producing appliances.

Only Competent Persons within their areas can install these
appliances:

•Gas safe
•17th Edition IET
•OFTEC
•HETAS

Boilers

Legal requirement
No matter which type or style of boiler is installed, the engineer
must be a registered Competent Person.

​Research and Identify the Requirements for Registering as a competent person scheme for the following:
Gas
Oil
Solid Fuel
Electric Boilers

Boilers

Boilers
Central heating systems today are generally heated by one of
four fuels:

•Gas (natural and LPG)
•Oil
•Solid fuel
•Electricity

Natural gas and electricity are supplied to the property via the
national grid, whereas LPG, oil and solid fuels have to be
delivered.

Boilers

Gas boilers
These are by far the most popular type of boiler and they can
burn either LPG (propane) or natural gas (methane based gas).

Traditional (non-condensing) boilers

or

Condensing boilers

Under Building Regulations part L, in the vast majority of cases,
only SEDBUK rated A condensing boilers can now be fitted.

Boilers

Gas boilers

Traditional boilers use one heat exchanger to heat up the
primary water and are less efficient, allowing the latent heat to
be expelled to atmosphere.

Condensing boilers use two heat exchangers to heat up the
latent heat within the system. This makes them far more
efficient, which is why Building Regulations part L requires them
to be fitted.

Boilers

Gas boilers

Traditional (non-condensing) boilers
Use a single heat exchanger
to heat up the primary water,
allowing the flue
gases and latent heat
to be emitted to
atmosphere.

Gas boilers

Condensing boilers
The increase in efficiency is achieved by the flue gases passing
over a second heat exchanger, allowing the gases to cool to 550C
and condensate the latent heat that is given off. Because of this
condensation, pluming
occurs from the flue and
provision has to be made
to drain the slightly acidic
condensate from the boiler.

Boilers

Gas boilers

Condensing boilers
Advantages:
•Compliant with Building Regulations part ‘L’
•High efficiency
•Reduction in system corrosion
•Quiet in operation
•Condensing combination boilers offer good flow rates
Disadvantages:
•Higher maintenance
•Disposal of acid condensate
•Use more gas if not in condensate mode

What Is A Condensing Boiler | Worcester Bosch

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Boilers

Gas boilers
These traditional and condensing boilers are available in three
main designs:

1.Conventional boiler
2.System boiler
3.Combination boiler

Compare the Positives and Negatives of the 3 boilers

Boilers

The SEDBUK rating
Seasonal Efficiency of Domestic Boilers in the UK outlines the
efficiency rating of boilers.

Generally only SEDBUK rated A boilers can be installed.

Open Ended

What does SEDBUK stand for?

Boilers

Gas boiler designs

Conventional boiler
Economical boilers for central heating systems. These are a
standalone basic boiler for which you need to purchase all the
system components, including the circulator, automatic bypass
and expansion vessel, if required.

If an open vented system is installed, a conventional boiler is
required.

What Is A Regular Boiler | Worcester Bosch

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Boilers

Gas boiler designs

System boiler
These are more commonly installed nowadays and include the
circulator, automatic bypass and an expansion vessel. This saves
time and space on the installation.

If a sealed system is required, a system boiler is the preferred
choice.

What Is A System Boiler | Worcester Bosch

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Boilers

Gas boiler designs

Combination boiler
Popular for small to medium properties, with instant hot water
under mains pressure, with a sealed central heating system.
Cold mains water passes through a plate heat exchanger in the
boiler and onto the tap. This replaces the need for a DHW cylinder,
CWSC and F&E.

Before installation the incoming pressure and flow rates at the
property need to be checked.

Boilers | Worcester Bosch

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Boilers

Gas boilers
Combination boiler
The limitations of a combination boiler should be outlined to the
customer before installation.

•Only supply DHW to one draw-off point at any one time
•Take time for DHW to reach temperature
•When DHW is demanded the CH circuit is cut off
•Flow rates are set by the manufacturer to gain required
temperature rise
•Scaling can occur in hard water areas
•No DHW back-up if mains is cut

Discuss the requirements for the two properties and analyse the system type to install

Using the floor plans

Boilers

Oil boilers
These tend to be installed in more rural areas and are also
available in conventional, system and combination boilers.
To be compliant with Building Regulations part L, a condensing
oil boiler will now need to be installed.

Boilers

Gas boilers
These are by far the most popular type of boiler and they can
burn either LPG (propane) or natural gas (methane based gas).

Traditional (non-condensing) boilers

or

Condensing boilers

Under Building Regulations part L, in the vast majority of cases,
only SEDBUK rated A condensing boilers can now be fitted.