Two weeks ago our antiquated Apollo 30/50B starting making a horrendous banging noise which made it pack up after each time it fired up. We had several no shows from plumbers and have only just been visited. The kind fellow changed the setting on the pump and now is fine, except....when the boiler fires up it makes a noise like a plane passing over the house (I think it sounds like a Hercules). I have bled all the radiators and checked the tank in the loft. Help!!