Ignition Devices

• Spark Igniters
  • Piezo-electric ignition
    • Fitted on gas fires, water heaters and older boilers
    • A plunger strikes crystal (quartz) and produces 6000v
  • Mains and electronic ignition
    • Uses step up transformer to create up to 10000v spark
    • Creates 4-8 sparks/second
• Filament Igniters - small coil of thin wire which glows red when energized
  

Appliances Thermostats

• Controls a burner when it reaches a pre-set temperature
  • Primary control - fitted within the appliance (controls heat input)
  • Secondary control - room thermostat
• Operation types
  • With a pilot light - will close completely
  • With a by-pass - will keep a low flame going

Rod Thermostat

• Invar rod (low thermal expansion) inside a brass tube connected at one end

Liquid Expansion Thermostat

• Flexible metal bellows connected to a hollow probe by a capillary tube
• It is full of either a gas or liquid
• The stat for a cooker has a by-pass tube

Electrical Thermostat

• Do not pass gas through their body
• Solenoid Valve is used to control the gas flow
• Bellows operated device - the most common
• Bimetal coil - room thermostat
• Bimetal strip - cylinder thermostat
• Should be checked using continuity testing (avoid live test)