Question

Reason geyser catching fire

Answer 1

geyser is a device that requires much current
as heat dissipation= I²RT
more I leads to more heat dissipation
sometimes It cross limit and due to overheating it catches fire.
sometimes there r others causes also like high voltage shortening etc

Answer 2

Due to some electric faults, short circuit, over voltage etc, there could be high currents in the electric resistance coil inside the electric geyser. The coil may not be affected.  But the electric plug, wire covering (plastics etc) could start burning if the temperature rises too high.  Sparks could result if the wires are loosely connected or the pins are close by or due to faulty conditions.  Rusted joints could also create possibilities.  Paints and easily flammable materials used in the geyser could catch fire fast.