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
  
  
  

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
  
  

Air-pressure Switch

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

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)