Worcester 240 Combi OF! Help

[highlander1403]

Hi Ya
Having problems with the above combi, basically it doesn’t work at the mo! Can light the pilot light and as soon as the switch is activated to go in to heating mode it lights the main burner in the combustion area for approximately 10 to 15 secs the goes out.
The flame in the combustion area seems to have excessive flames (set on min & max) and within this short period the pilot light flicker continuously then the system goes out.
Obviously any guidance/help would be much appreciated and yes I did have it serviced about three months ago

[lisdar]

Sounds like the fan is not running or combustion chamber or flue blocked
and blowing back is the flame you can see

[htg engineer]

Worcester 240 OF - open flue ?
Fan ????? there wont be one.

Check pump, if heat isn't getting away from boiler it'll cut out, excessive flames ? check diverter may be stuck in hot water mode - will be higher gas rate also heat cannot escape without tap being opened - so diverter may be the problem.

htg