My Worcester 9.24 electronic boiler has stopped working.?

Sounds like either your hot surface ignitor is out or your flame sensor is dirty not allowing burner to ignite. There should be a site gl or window that you can see the ignitor y. Watch at start up to see if you can see the ignitor starting, it will glow red hot if working. If it does and it lites then goes off after a few seconds then your flame sensor it dirty and needs to be cleaned. These arent difficult things to do yourself.. If not comfortable then call your HVAC contractor. Hope this helps