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Gas Appliances

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

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Boiler Controls

Permanent Pilot

Upperplumbers_parts_for_gas_boiler.jpg permanent_pilot
  • gas is supplied to the inlet of the multifunctional valve (gas valve)
  • a piezo igniter is used to light the pilot
  • the pilot heats the thermocouple which connects to the gas valve
  • a thermostat calling for heat then gives power to the gas valve to open
  • the main burner receives gas
  • if the pilot fails - the thermocouple cools and closes the gas valve
  • the boiler thermostat controls the temperature of the water by opening and closing the gas valve

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Intermittent Pilot

  • the boiler thermostat calls for heat
  • the control board activates spark ignition
  • spark occurs at the pilot assembly
  • the pilot solenoid opens to let gas through to pilot
  • the pilot ignites and the ignition electrode detector senses flame
  • the spark stops and the main solenoid opens
  • gas flow to the main burner and is lit by the pilot

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Air-pressure Switch

  • safety cut-off device for fan-flued boilers
  • prevents the boiler lighting sequence in the event of the fan not operating
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Overheat Thermostat

  • MUST be fitted with any boilers used for sealed water-heating systems
  • wired 'in series' with thermostat
  • Water-pressure switch
    • controls the operation of the pump
  • Multiple controls are controlled by a number of printed circuit boards (PCBs)
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