happen at any part of the mains cycle including those times when the mains voltage is near zero the spark detection circuitry cannot hope to pick up every single spark in practice though disconnections which occur near the mains zero voltage do not have significant energy for ignition it is practical to detect 75 of all heater wire disconnections and this provides the required degree of safety in a first embodiment of the invention a two winding transformer is connected in series with the heater wire as can be seen in fig2 during normal operation the current flows from the ac supply 1 through the primary 2 of the spark detection transformer then through the heater wire 3 if a break 4 occurs in the heater wire 3 causing sparking a rapid change in current will occur in the heater wire 3 any rapid change in current through the primary winding 2 of the transformer creates a voltage spike due to the action of its inductance the voltage spike is passed onto the secondary winding 5 of the transformer and is multiplied by the turns ratio the voltage spike on the secondary winding may be either positive or negative but the four diodes form a bridge rectifier 6 so that the voltage spike always charges the capacitor 7 with a positive voltage if the magnitude of the voltage spike is large enough then the capacitor will charge above the threshold voltage 8.