The guy came round and checked everything in about 20 mins and then said that the only thing that he couldn't test was the PCB and told me to speak to Baxi. I did and they want to charge £300 to send someone round.
Cheers for the reply - the condenser was checked and was draining normally but it seems strange that the burner fires if left off for a long period of time. Is it worth getting someone to check it more closely?
Posting this because Baxi have been useless. Boiler is 13 months old and the burner fails to light after the fan has started. I can sometimes get it started but only on maxumum and if the burner stops for any reason it will not relight for several hours/days. An engineer has visited but couldn't...