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Gas Safety

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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Chimney and Flue


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Safety Devices and Controls

Air/Gas ratio valves

Appliances Controls

Flame Supervision Devices FSD

Gas Controls

Gas Meter Controls

Safety Cut-off Devices

Spare Part Identification


Open-vented System


Gas Appliances

Ventilation Sizing

Unsafe Situations

Dealing with Unsafe Situations

Emergency Notices and Warning Labels

Gas Leak




Tightness Test

Gas Performance

Gas Rate

Heat Input

Gas Supply

Gas Meters

Gas Pipework

Gas Fittings and Pipes

Gas Supply


New Installation

Pipe Protection

Pipework Sizing

Chimney and Flue


Flue Construction

Flue Inspection and Testing

Flue Terminals

Flue Types


Carbon Monoxide Poisoning

Combustion Process

Natural Gas

Portable Combustion Gas Flue Analysers


Components and Safety Devices


  • The chimney may be constructed of
    • Gas flue blocks to BS1289
    • Chimney blocks to BS6461
    • Factory-made insulated chimneys to BS4543
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Unlined Chimney

Unlined Chimney connection
  • High level connection:
    • Seal the break chimney between 250mm and 1000mm
    • Provide a means to clear debris from the catchment area
  • Base/recess level connection:
    • MIN 75mm clearance between the outlet and chimney wall
    • MIN projection of an appliance into the chimney is 250mm
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Solid Fuel Chimneys

  • Suitable for gas and oil fired appliances
    • Restrictors or damper plates should be removed or secured in the open position
  • Recess
    • 200mm - minimum back thickenss (jamb)
      • Could be reduced to 100mm if serves two recesses
    • 690mm - 840mm - with of the recess, adequate for all gas appliances
    • 350mm - depth of the recess
  • Hearth
    • Constructed of a concrete
    • 125mm - minimum thickness
    • Must extent fully into the fire recess
    • 500mm - minimum projection in front of the jambs
    • 150mm - minimum projection on each side
    • 'Baxi overnight hearth'
      • Has a duct which comunicates a ventilated floor void
      • Must be sealed prior to the installation of a gas fire
  • Lintels and Throat Units
    • Triangular in cross section to avoid obstructing the flow of smoke
  • Fireback
    • Heat-resistant fire clay is built into the rear of the fire
  • Flue Systems New Installations
    • Flue must contain a clear circular space of minimum 175mm
    • 45° - maximum offset angle
    • Flue must be lined
      • Clay lining BS EN 1457
      • Rebated and socketed kiln-burnt aggregate and high alumina cement lining
      • Rebated and socketed clay pipes and fittins to BS65
      • Flexible stainless steel linings are not recommended
  • Flue Systems Existing Installations
    • An existing 225x225mm brick chimney - suitable for new appliances
    • Chimney built befor 1965 may not be lined
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