You do not need a new boiler. Your boiler needs a proper service now and then. If this is not done, some parts get sluggish. This is what (I suspect) has taken place.
When you make a demand on the boiler, the boiler mechanics operate sequencially. For code 03, fan gets powered up, it draws air from the combustion chamber (where the fire would be). The movement of air across a component known as venturi causes a switch to operate. This switch is not operating. Does not mean the switch is faulty, more like the guy did not know what causes 03 code to be displayed.
Is a good idea to be in the room while work is being carried out. If he is all thums, he will start to sweat. If he is good, does not appear to be, he will 'show off' how good he is with positive results and effect good repairs too.
Good luck. If you need more info, send a PM
