hi,i have a worcester boiler 24i/28i and it is not working,it is not providing hot water or heating,i dont think the pilot light is on as it is not firing up as normal,it says in the instruction book that if the overheat cut off has operated the fan or pump will run but the burners will not light, (no spark generation),it says the appliance can be reset by pressing the overheat cut off button,it has a button at the top of the heater but it is more like a plastic screw rather than button as there is nothing to press in,i just wondered if anyone would be able to give me some help on this...