Emptied condenser syphon on Greenstar 24i but still not working ?

I have just re-read your question saying that you have cleared the syphon, 'the water in the boiler casing' might be your issue now.
If you have a 'Prettle' gas valve (the connections are on the back of the valve), the lower connection could be sat in the water, this will also cause lockout.
You will need to dry thoroughly (I use a hairdryer in such cases) to completely disperse the lying water.

Carefree
December 2010

Try the actual condense trap inside the boiler, on the greenstar, they tend to block with a grey sand (from when the main heat exchanger was cast), clear this out, and hopefully, you'll be sorted.

Carefree
December 2010