Ahh okay, sorry for delayed response. A powerful wall, axial bathroom fan will have to do then. I see somebody else has already recommended The Envirovent SIL100, which I would 2nd!! Great fan, lots of different variants too...
Airflow Inline fans from experience have always been great and worked well and well outlasted their warranty. What I would say though for the price you may pay to repair you may as well replace as the extractor fan technology and abilities have increased since the AV100T model was released. This...
Another way is looking at installing an inline extractor fan, I know you have a fan installed but if you have space above in the void/loft these are three times the power of a wall mounted bathroom axial fan. As they are installed outside the room they are just as quiet too...