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Gas Appliances

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

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Water Heaters



  • Small Instantaneous Water Heater
  • The water heater has an open end, usually in the form of swivel spout
  • Incorporates a flame-failure device - a thermocouple which is activated by the pilot
  • Should the pilot flame fail then the thermoelectric valve will close
  • On most new appliances a thermal switch and ASD are built in to prevent overheating and operation if the oxygen levels fail

  • Automatic valve - turns gas on when a tap is opened and turns the gas off when is closed
    • works on the principle of 'differential pressure', using a venturi

  • The temperature of the water can be controlled by a thermostat in larger models
    • Temperature Selector - the simplest form of temperature control
  • The 'slow ignition device' allows the main burner to light safely and quietly and closing the burner quickly
    • 'Loose ball' type - situated in the low pressure side of the diaphragm
    • Screwing the device in or out regulates the amount of water that can bypass the ball and so adjusts the rate at which the diaphragm lifts

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