Bathroom fan not turning off

In harmonised three-core-and-earth, colours identify the core—not its function: - brown, black and grey are all potentially line conductors; - black should be brown-sleeved if used as a live; - grey should be blue-sleeved if used as neutral. Do not rely on terminal position matching the old unit. Check the moulded markings on the new Manrose carefully: permanent live is normally L, trigger is normally T, LT, or SL. - A like-for-like physical replacement can still have a different terminal arrangement. I don't recommend doing a very quick check under live conditions to see which core is neutral, switched live, and permanent live. This method is to check voltage(potential difference) between the cores, if both conductors show 230v to one common conductor then the common one is neutral. Then switch off and check which conductor is dead. Moreover it's inaccurate and dangerous especially when there's a borrowed neutral. Recommended way to do it is to identify the circuit, safe isolate the circuit, and then do end to end conductor tests to identity which one is which.