hi i have a problem with my kingfisher potterton 2 boiler or hot water tank which is my loft the tank that is when the hot water comes on my tank in the loft is making a thundering rumbling noise the boiler is 15 years old my tank is 27 years old does anyone know if i would need a new boiler or a new tank or would there be something that might be cheaper to put this fault right i can hear this noise down stairs and find i have to turn the water off