Just had a new Vaillant eko 428 boiler installed and when it starts up it 'roars' for approx 30 mins. When it settles down it still appears to be more noisy than expected. I have listened to a recently installed Worcester boiler and that is quiet on start up and quieter when running than the Vaillant. Is this typical with this boiler, or a problem either on the installation or boiler fault. Help!! Thanks for any feedback