boiler keepcutting out when itget hot?

2 02 is no flame detected.
This could be an issue with the gas valve or electrode, but a more likely cause would be condense failing to clear the boiler properly, this would be consistent with your 20-30 minute period of operation, followed by the same sort of 'downtime'.

Check the condense trap and pipework to ensure it's clear.

Carefree
March 2011