Your boiler is failing to ignite because it isn't receiving enough gas or water flow to start the heating process.

Technical description

I) Gas service tap not open fully; II) Gas pressure low; III) Water rate low; IV) Gas valve not opening; V) Diaphragm punctured; VI) Venturi blocked or loose; VII) Gas control tap faulty; VIII) Wrong injector; IX) Slow ignition device stuck or wrongly adjusted