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Gas Appliances

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

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Types of Gas Fired Boilers

Floor-standing Boiler

Domestic boilers have an output of between 9kW and 70kW
Many boilers have 'range-rated' burners - they can be adjusted to suit the size of the system

  • Free-standing boilers were fitted in kitchens
  • Cast iron heat exchanger
  • Open flued
  • Uses a permanent pilot as its source of main burner ignition
    • Piezo unit lights the pilot burner
  • Multifunctional valve incorporates:
    • Constant pressure governor
    • Flame supervision device (thermocouple)
    • Solenoid valve
  • Pilot assembly incorporates:
    • Pilot burner (injector)
    • Thermocouple
    • Spark electrode
  • Boiler control thermostat electrically connected to the solenoid section of the multi-functional valve
    • Responses to water temperature fluctuations
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Wall Mounted Boilers with Fanned Flue

wall mounted gas boiler
  • heat exchanger may contain as little as one litre of water 'low water-content' boilers require a positive flow of water at all times
  • Pump overrun thermostat - to remove the residual heat from the heat exchanger

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Natural Draught Open Flued Back Boiler

back boiler
  • Limited heat output - 15kW
  • All pipework MUST be protected against corrosion from falling soot
  • Atmosphere (vitiation) sensing device ASD must be fitted
    • Extinguishes the pilot and eliminates gas flow to the burner in case of incomplete combustion
    • Incorporates combined thermocouple/atmosphere sensing device
  • Takes combustion air from teh space it is located
    • Lint arrestor - prevents lint from entering teh main burner
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Combination Boilers

  • Combination Boiler is an instantaneous water heater
  • any hot water demand takes priority over the central-heating demand.
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Condensing Boilers

  • 94% efficient
  • use the heat from flue gases 175-250°C by means of extra heat exchangers
  • Flue gases - 75°C
  • Condensate is a weak acid
  • The flue system MUST always fall back
  • BS 6798 - condensing pipe installation
    • MIN 22mm pipe
    • MIN 75mm seal
    • 50mm/m - MIN fall
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