Posted: 18/12/2012 at 18:18
Jo, with your boiler, you deffo need to get engineers to check it out, the first 30 - 50 mins after firing up is when there is the most demand on it ( it runs at its highest capacity during this time to get the system up to temperature quickly), three possible things spring to mind,
1. scaled up heat exchanger but I have discounted that as it's a new boiler.
2 it needs the burner pressures / combustion mixture adjusting
3. there may be a restriction in the flow,
You need an engineer with the correct analyser equipment to check and adjust the mixture but you can do a basic check on the flow yourself, try opening up all the radiator valves to max and see if it alters / stops the noise, hope this may help you pinpoint the problem.