If the electrodes fail to start combustion, a photocell comes into operation. The photocell consists of a light sensitive resistor whose signal is monitored by the control box. Should the boiler fail to ignite after a pre-determined period then the control box shuts off the oil supply and ‘locks out’. In most boilers ‘lock-out’ is indicated by a red or orange neon light and a button is pressed to re-set the burner control system. .
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