WIRING EXTRACTOR FAN-only switched by isolator switch NOT light switch

[gooty]

My bathroom extractor fan (in the attic) is wired correctly with an isolator switch (in the airing cupboard), using 4 core cable where necessary for the fans timer to work when the light is turned on/off.
However, I want to change it so that the isolator switch is the only switch used to turn the fan on/off, and the light switch has nothing to do with it.
I want to do this because the timer on max doesn't run long enough to get rid of the condensation, and I have to either keep going back upstairs to turn the light on/off every 20 minutes or waste electricity leaving the light on.
I think I've figured out how to do this, but want to check first as the 4th timer wire is bit puzzling to me. I assume that although the fan already has a PERMANENT LIVE/NEUTRAL going into it, the SWITCHED LIVE tells it to start and keep running as long as the power from it is still there. Then switching off the SWITCHED LIVE lets the timer only continue running for the extra pre-set time before it completely turns off again.

I was going to do this in the isolator switch:
1) Remove the 4 core black SWITCHED LIVE IN and insulate it.
2) Run a second extra wire out from the PERMANENT LIVE OUT and loop it around and into the now empty SWITCHED LIVE IN.

Is this correct as it seems too easy?

[Neelix]

Why don’t you adjust the over run timer on the fan?

As for leaving the light on that’s peanuts

Do you have enough airflow into the bathroom ?

[Someone-Else]

I would say it sounds like you do not have enough "through flow" of air. (As Neelix asks)
I would check that the bathroom door is left ajar, or there is a 2cm gap under the door, also I would check the duct run, and the inside and outside grille to see if any either or all are blocked/covered in lint.

[gooty]

Thanks for the replies but I've checked these and wanted to try this as a last resort.
Plus
It would be handy to have lights on without the fan going in the summer.
Does anyone with electrical knowledge know if the way I want to wire it will work?

[Neelix]

Thanks for the replies but I've checked these and wanted to try this as a last resort.
Plus
It would be handy to have lights on without the fan going in the summer.
Does anyone with electrical knowledge know if the way I want to wire it will work?

You seem set on the least practical solution ….. with a longer over run and good proven airflow you could simply switch the fan off in the summer

[gooty]

The timer is turned to max (or alternatively I can leave the extractor running for ages with the light on), the outside vent mesh is clear and I've tried with both the window and door open and still no difference to extraction. The fan easily sucks a piece of A4 and holds it over the inside vent. To sum up, it appears to have loads of suction but it's just not enough. My family insist on having the bath water at a crazy hot temperature so there's condensation on all walls, mirrors, radiator etc. I just need confirmation about the wiring alteration above if anyone has the knowledge? Thanks

[gooty]

no worries, I rewired it as above and it works as expected now.