Extractor fan timer woes

[steenjo]

Hi. I know there have been posts on this topic here before, but I can't see my specific issue addressed. I'm replacing a bathroom extractor fan. The old one [EnviroVent silent 100] worked fine including the timer overrun, but I'm redecorating so I thought I'd replace with a better looking and apparently quieter product i.e Expelair C4HTSR. I installed the new fan but the overrun didn't work; the light and fan were both on when they were on but turning the light off also turned the fan off; no overrun. So I sent the fan back and got a new one from somewhere else. Exactly the same problem.
The wiring to the unit has a brown wire, a grey wire and a black wire. I am wiring the new unit the same as the old, that is brown to 'live', grey to neutral and black to switched live. This wiring worked fine with the old unit. When I test with a meter I can see there is current between brown and grey when the light and fan are on, and current to brown and black (switched live) when I turn the light off. So there is current but no overrun. Given this has happened with two different units now it seems unlikely the unit is at fault. The real strangeness is that I tried putting the old unit back and this is now doing exactly the same thing even though I've wired it back just as it was before. I am now doubting my sanity. Has anyone got any ideas?

[wine~o]

Swap the brown and black around at the fan.

Lecky off first

[Someone-Else]

The real strangeness is that I tried putting the old unit back and this is now doing exactly the same thing even though I've wired it back just as it was before.

Clearly you didn't (You connected it as you thought it should be.)

There is no specific colour code for lights/lighting, it is up to who installed it what colour they used for what.
A good reason to take a clear in focus picture BEFORE you do anything. (Labelling also helps)