​Scope (P14.1)

​BS 6798 specifies the requirments for the selection, installation, inspection, commissioning, servicing, repair and maintenance of both new and previously used gas-fired boilers used for wet central heating and other purposes such us hot water.

It applies to 1st 2nd or 3rd family Gases.

total heat input not exceeding 70Kw

​BS 6798 also applies to cookers with integral C/H

For BBUs, additional information is contained in BS 5871 parts 1 and 2.

BS 6798 does not apply to individual boilers with a rated input greater than 70KW net, but with an aggregate heat input in excess of 70kw net. In these cases, BS 6644 and IGEM/UP/10 applies.

Groups of boilers with an individual heat input less than 70kw net, but with an aggregate heat input of 70kw net or less, may be installed to this standard, however specialist advice will be required from the appliance manufacturer with regards to system design, control and installation requirements

Regular Boilers

• Normally referred to as HEAT ONLY

• Do not have an internal facility to provide DHW

• Separate hot water storage system is used for this purpose

Combination Boiler

• Provide both heating and hot water as part of their design

• Instantaneous or stored

How A Heat Only Boilers Heat The Radiators.

• The primary heat exchanger,

which heats the cold water
that flows through your pipes
and then warms the radiators.

• The water that passes through

your central heating pipes is
returned to the boiler.

How hot water Heated with a Heat only Boiler

• Stored hot water is heated by being separate water being pumped though a Boiler Heat Exchanger and a coil in side the cylinder.

• Mains feed or tank fed

Back Boilers

Heat Only Boilers

DHW Storage
unit can be

Open vented

or

Unvented

​Open vented system

​System

Boilers

1. ​What is System

Boiler?

What additional external controls would be found in a System Boiler?

​Pressure reducing valve

​Pump

​Expansion vessel

Low-water pressure switch

​Heat exchanger

​Filling Loop

Additional external controls that would be found in a System Boiler

​Pressure reducing valve

​Pump

​Expansion vessel

Low-water pressure switch

​Filling Loop

Combination

Boilers

This Photo by Unknown Author is licensed under CC BY-NC-ND

Combination boilers, known as combi

• Provides heat for C/H and DHW

• Eliminates the need for a
separate storage vessels or tanks

• Mains pressure at all hot water

outlets

• Modern boilers are now condensing

Hot Water

• The DHW is taking water from the mains and being heating via a boiler heat exchanger.

• Note:- If you have a combi boiler the hot water takes priority, therefore the heating will switch off when there a demand for hot water.

Condensing technology is simply a way to extract
more heat from exhaust gases that used to be
wasted in older non-condensing boilers.

How A Condensing boiler

Boiler Works

https://youtu.be/7c_ZAVnhTeI