Fan Isolator & Light Switch Change

On Holiday · 27 Dec 2025 at 13:42

Hello, DIY-dave here.

I'm down to the last couple of switches being replaced and have been stumped.

I have a couple of bathrooms which have these switches on the outside.

They operate independently, the fan has no overrun timer and is instant off/on with the switch.

I therefore naively thought (before lifting the cover) that I could just replace it with a double light switch but upon taking it off and looking at the wiring, confusion set in.

I can't find a 2-gang DP to replace this with.

Any suggestions? I'm open to doubling up the fan & light into a 1-gang DP so they come off/on at the same time but not sure how wise that is.

K.C. Leblanc · 27 Dec 2025 at 21:39

There are modular systems like the MK Logic grid system that let you build a multi gang switch in any combination.

EDIT, linky goodness. https://www.tlc-direct.co.uk/Products/MKK3632.html

Jasoncmor · 27 Dec 2025 at 22:29

Its hard to be certain without seeing it first hand, however, what it looks like to me

Top left L2 - 2 x browns are the mains in and mains out, with a mains link that comes out and takes a mains (live) to the right hand L2
Bottom left L1 looks to be the switched live going to your fan, the brown sleeved black cable in N1 on the left looks like its possible a switched live which also goes to the fan, or another circuit, but without knowing more its impossible to tell.
Right hand L1 goes to your light.
Not entirely sure what the link between the top left N2 down to the bottom right L1 does, maybe some kind of over ride or extra circuit for the black?
When you switch your light on, you have a live that goes through the N2 and out down the black cable
It could be worth opening up your fan to see what cables you have present.

Also, you dont need any double pole switches as you are not switching any neutrals.

wonko · 28 Dec 2025 at 14:14

From the rear, it looks like:
Left L2 is incoming live
Left L1 is permanent live to fan (if not isolated) to support overrun
Right L2 is the linked incoming live
Right L1 is switched live to the light
Left N1 is the switched live to the fan
IIUC, current wiring regs expect a 3-pole isolator for the fan (permanent live, switched live and neutral) and possibly a fuse. As it stands, if the light switch was on and fan switch was off, someone could get a nasty surprise thinking the fan was isolated.

Jasoncmor · 28 Dec 2025 at 16:11

@wonko
I believe fitting an isolator would only apply to new installations, existing installs would be exempt, as it would have been installed correctly at the time, according to the current wiring regs of that time.
It wouldn’t hurt however to install a fan isolator if at all possible.

On Holiday · 28 Dec 2025 at 18:04

Thanks for the comments all.

My missing search phrase was "grid switches" apparently, although I still can't find any that I like the look of so I might just plastidip the existing ones to see if it improves it, before completely giving up and replacing it with something - one way or another.

Both fans could do with an overrun timer, so might expand the scope to do that too.

Jasoncmor · 28 Dec 2025 at 20:24

On Holiday said:
Both fans could do with an overrun timer, so might expand the scope to do that too.

You would need to replace the fans for that, assuming they don’t have the option already.
However, if they did have overrun, and weren’t connected, the fans normally wouldn’t run with just the one live connected.

wonko · 29 Dec 2025 at 08:49

Jasoncmor said:
@wonko
I believe fitting an isolator would only apply to new installations, existing installs would be exempt, as it would have been installed correctly at the time, according to the current wiring regs of that time.
It wouldn’t hurt however to install a fan isolator if at all possible.

I believe you're right about not having to bring it into line with current regs, but it wouldn't be a bad thing to do if there's opportunity.
p.s. My comment about the fan getting a live when the fan isolator switch was off was wrong - not sure what I was thinking there.