Extractor fan wiring question

[EH75]

Afternoon all.

I have been up in my loft over the last few days dealing with the ducting in my extractor fan after discovering a small swimming pool developing up there. After much faffing with rigid ducting and insulation I hope I have sorted it out.

Anyway whilst I was up there I thought I'd have a look at how the extractor fan was wired up. The fan has a timer function so it should keep running for a while after the switch is turned off but this has never worked. I understand these are usually designed to be connected to the lights but I specifically asked them not to do this when they wired it up as there is nothing worse than getting up for a pee in the middle of the night and having to listen to the fan for 10 minutes afterwards! So the fan has its own switch next to the switch for the lights. However when you turn this switch off, the fan goes off immediately without the overrun. See below wiring:

Fan (can't see in the photo but terminals are marked as L / N / SL as you look at it)



Isolator



Switch (the fan switch is on the left when the faceplate is screwed into the wall and you are looking at the front of it, lights on the right)





The fact this didn't work properly never initially bothered me but given the issues I've been having with condensation recently ideally I'd like to have the timer working (without connecting it into the lights so I an still use the lights without running the fan) so that it clears the ducting a bit better and hopefully reduces any condensation forming. I doubt I will be doing this myself and will get the electrician to have a look at it next time I am having work done however I am curious to understand how its been wired up and why it doesn't work as it should. Presumably it is missing a permanent live? But why? There is a black wire you can see in the photo of the wiring on the fan itself which is not connected to anything. I thought this might be a live so I tried connecting it up but nothing happened. That's probably about the limits of daft messing around with things I don't really understand that I will be doing but I am still curious to have a bit of a better understanding as to what is going on here.

 

[EH75]

When I did one last, it had a humidity setting in it so it would come on automatically when it detected any, normally not long after turning the shower on.

What make and model is it? You should be able to look up the wiring requirements online for the one you have. Was there any other switches/jumpers on the circuit board that could control the timer function?

Its a Manrose MF100T.

The extractor fan is wired incorrectly for timer function, a timer function needs Switched live, neutral and permanent live. Your has only S/L and a jumper to L so as soon as you turn off the switch the extractor isn't getting any power.

This is pretty much what I thought. My question is why is there not a permanent live on the circuit? I thought that might be what the unconnected black wire was so I tried wiring it in but that made no difference. I suspect the black isn't connected to anything at the other end? I guess the way to remedy this would be to connect the black wire to permanent live at the other end then wire it into the fan? Or am I way off in my thinking here?

 

[EH75]

You need to take a feed from one of the common terminals at your light switch and put it in with the black thats in the red wago connection at your light switch. Remove the brown link at the fan and put the black in its place.

It's not a simple mistake to make, gross incompetence from who ever fitted it.

So like this basically?



Regarding what was originally requested, I merely didn't want the fan to come on with the light and wished for it to be controlled with a seperate switch. I still wanted the timer to run. I obviously should've questioned this at the time but it was a couple of years ago now and I can't remember why I didn't. Had a lot going on at the time.

 

[EH75]

No you want the black wire to go into the lower terminal on your switch instead of the brown wire that's currently in there. This now becomes your switched live to the fan. The brown wire that you've removed goes to the common/constant live on you're switch.

At the fan take out the brown link wire. Double check the fan terminals and wire it as brown - constant live, grey - neutral, and black - switched live.

Your fan will then work as you want, so it will turn on when you flick the switch on and when you turn the switch off it'll run on the timer then turn itself off.

So I did this, and it now works as you would expect in that when you switch the fan off it will continue running on a timer. HOWEVER, it now also runs at random with the switch off. So with the switch off it will turn itself on for about 20 seconds, then off for 10 seconds then this repeats indefinitely. Bit weird no? The only way to shut it off completely is to turn off the isolator switch. This obviously defeats the purpose of the whole thing. So I have put it back to how it was wired originally. See below for how it was wired up when this issue was happening:





Any ideas what is going on here?

 

[EH75]

The jumper on the right is for the fan speed (there are 3 speeds, it is set to the highest one). The screw adjustment on the left of the circuit board is for the overrun timer adjustment and is set for the maximum time. This model does not have a humidistat. In any case even if it was a humidistat model, it still shouldn't come on with the switch turned off I wouldn't have thought?

 

[EH75]

So, an update on this. I got back up there and tested everything with a multimeter. Live showing 240V (obviously). Switched live shows 20V with the switch off and 240V with it on. Seems correct no? Anyways, I managed to obtain a replacement fan from Manrose free of charge under warranty as the fan was also exhibiting other strange behaviour such as stalling when it had been on for a while. So I suspect it was dodgy. The new fan I have wired in and it all seems to be working ok so far including the timer function and no random turning on and off. Still wondering what would've been causing the issue previously with the old fan randomly running and turning itself off? I guess maybe the capacitor that runs the timer not working as it should, holding the charge for too long and then discharging at random, instead of all in one go? Those probably aren't the correct terminology but you get what I mean.