sime 90 gas boiler ?

if u can see the blue spark it wont be the igniter. if it fires up and u can see the flame and it still keeps clicking then the flame electrode needs cleaning with sand paper. if there is the blue spark and no flame then the gas valve is on its way out. u may need to check the pcb if the gas valve requires changing to make sure the correct voltage is at the gas valve before changing the valve.

kash
March 2013