2004 Vauxhall Astra starting problem

i start from cold first thing in the morning , no problem, drive for say 30 minutes up to 1 hour or so, park up switch off, try to start engine again between 20 to 30 minutes later, it will not start so i turn off key and open bonnet and wait for the engine to cool a bit for say 20 minutes then turn the ignition on to turn and start the engine it works then and fires up the local vauxhall garage has checked out for fault codes etc but it shows nothing strange if anyone has any ideas please help