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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

Flue Construction

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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

Twin-wall Metal Flues

Twin-wall Metal Flues
  • 2 types:
    • With an air gap between the walls
      • external use on longer than 3 meters
    • Fully insulated pipe
  • Suitable for all fuels for appliances that operate up to 600°C
  • Sleeve must provide minimum 25mm of gap (filled with non combustible material) when passing through combustible material
    • Metal ceiling and metal floor plates used as a seal
  • Spigot should face up words
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Vitreous Enamelled

Vitreous Enamelled
  • Internal use only
  • Socket faces up words
  • For making connections from:
    • wood burning stoves
    • cookers and heaters to chimneys
    • flexible liners and flue systems
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Flexible Stainless-steel Flue Liner

Flexible Stainless-steel Flue Liner
  • Used to line an unsatisfactory existing chimney
  • The top and the base of the chimney must be sealed with flaunching and sealing plate respectively
  • When chimney exceed a certain length they will require lining:
    • Gas fire (with or without circulator)
      • >10m for external wall
      • >12m for internal wall
    • Gas fire with a back boiler
      • any length
    • Circulator
      • >6m for external wall
      • >1.5m of external length and total length > 9m
    • Other appliances
      • >12m for internal
        • >20m
        • >33m for double wall 125mm metal chimney
      • >10m for external
        • single wall 125mm metal chimney not allowed
        • >28m for double wall 125mm metal chimney
  • Class 1 - Wood And Coal Burning (>250°C)
  • Class 2 - Gas And Oil Burning (<250°C)
  • 225x225mm flue opening
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Pre-cast Concrete Blocks

Pre-cast Concrete Blocks
  • Must have minimum 3 starter blocks
  • Built into the wall during construction
  • No excess jointing material left inside flue
  • Maximum offset of 30° using a raking block
  • Connected to the ridge terminal with a twin-walled insulated pipe
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Catchment Space

  • Minimum 42litres - volume of the void
  • Minimum 15mm - flue spigot protrusion
  • Minimum 50mm clearance - between the spigot and the back wall
  • Any appliance fitted to an unlined brick chimney or lined brick (flue block/metal) chimney (used for solid fuel or oil):
    • Minimum depth - 250mm
    • Minimum volume - 12 litres
  • Any appliance fitted to a lined brick or flue block/metal chimney new or unused, or previously used with gas
    • Minimum depth - 75mm
    • Minimum volume - 2 litres
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Flue Gas Collector Box

Flue Gas Collector Box
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Flue Height Calculation

Flue Height Calculation

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Fire Stop Plate

Fire Stop Plate
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