Vokera Compact 24 Fault (Red light)?

My boiler keeps tripping to internal fault (red light) after it has been on for a hour or so. It only appears to do this when in auto mode and set up with the clock?. Once reset the boiler works ok water and heating. I have set the position to auto and it does not seem to go on to the internal fault mode. Pressure is ok etc. Any ideas would be appreciated.

Lee Smith
January 2009