Wiring a run-on bathroom extractor fan - PLEASE HELP!!!

Hi

We're replacing a bathroom extractor fan. The old fan was cosmetically damaged and unfortunately got taken out (wife!) without me being able to label the wires.

New fan has a run-on function (timer and a humidistat) and it's totally doing my nut trying to get it to work properly! Please help before I have a breakdown!

The existing wiring from the old fan is 3-core and earth (colours are blue, red and greeny-yellow plus unsleeved earth). There's a normal pull switch for the light and an isolator for the fan and another for the light. The property was built in about 2002.

If I wire up the new fan one way then it runs normally when the light is switched on but then powers off as soon as I switch off the light.

If I then switch the positions of the two live cables (i.e. red and yellow/green) into the fan then it just runs continuously regardless of what position the light switch is running.

I'm a bit stumped - clearly there is a working switched live (the fan can be controlled by the light switch) and a working permanent live (the fan can run continuously). But why isn't the perm live kicking in when the switch live turns off?

My confusion got worse, in fact, when I tried a multimeter on the cable - neither of the live cables seemed to react at all to the switch being pulled (i.e. both cables showed no resistance across the blue neutral in either switch position). But clearly there is a working switch (the fan (and lights) respond to the switch being pulled).

Please advise - I'm starting to lose my mind!

The greeny yellow is yellow and likely to be the Switched Live (although could be Permanent Live).
Vice versa for the red.

If you get the PL and SL the wrong way round the fan will only work when the light is on.
Either way it should not run continuously without the light.

The blue should be Neutral.

The bare should be sleeved Green&Yellow and is Earth.


Was the old fan a timer model?

Thanks so much for getting back to me!

The old fan (an old model Greenwood Series 90 HT) also had a humidity sensor/timer.

It should work one way round or the other.

Many an hour wasted on faulty new items.

Thanks again.

Actually I thought the same (faulty new unit) as you so took the replacement fan back to the store and got another unit of the same model but had the exact same problem.

So back at square one - any ideas?

barry101 said:

If I wire up the new fan one way then it runs normally when the light is switched on but then powers off as soon as I switch off the light.

Click to expand...

That would mean they are the wrong way round.
Also it means the wire you have in the PL is actually SL.
So presumably in SL is actually PL or also SL.

If I then switch the positions of the two live cables (i.e. red and yellow/green) into the fan then it just runs continuously regardless of what position the light switch is running.

Click to expand...

That means both wires are PL.

I'm a bit stumped

Click to expand...

So am I.
As you can see and have deduced, that's not really possible.

clearly there is a working switched live (the fan can be controlled by the light switch) and a working permanent live (the fan can run continuously). But why isn't the perm live kicking in when the switch live turns off?

Click to expand...

Precisely.

My confusion got worse, in fact, when I tried a multimeter on the cable - neither of the live cables seemed to react at all to the switch being pulled (i.e. both cables showed no resistance across the blue neutral in either switch position). But clearly there is a working switch (the fan (and lights) respond to the switch being pulled).

Click to expand...

There wouldn't be with the power off.
Red and Yellow would be connected when power off but switch on. Try that.

If you are comfortable doing it -
Put all four wires into separate connector blocks and measure the voltage across
Red-E,
Red-N,
Yellow-E,
Yellow-N,
Blue-E.
whilst someone operates the switch.
If not comfortable you will need an electrician.


Many more hours wasted on second faulty new item.

Hi EFLImpudence

Just wanted to say thanks so much for the reply. Really is hugely appreciated and very kind. Thank you.

I'll need to pick up some connector blocks and will check as you recommend.

FWIW, I also tried the connection across yellow and red - there seems to be no resistance with the switch in either position. Does that make any sense at all?

Thanks again, anyway. Really kind of you.

barry101 said:

FWIW, I also tried the connection across yellow and red - there seems to be no resistance with the switch in either position. Does that make any sense at all?

Click to expand...

Not really because they should be connected when the switch is on.

Also the fan wont or shouldn't work with power only to PL or only to SL unless the internal electronic switch is permanently stuck on.

When you have bought the connector blocks, you could try connecting a light to Red, N&E then Yellow, N&E to see what works how.

Thanks again EFLImpudence for all your help. You are a genius and incredibly generous. Sincerely, thank you.

Tested all the cables as you advised and they all seemed to be normal (yellow was switch live).

Almost accidentally, and beginning to despair, I did resolve it in the end and thought I'd share it in case this ever is of any help to any other forum users.

When the fan (an Envirovent Silent 200) is first installed and the power switched back on, the fan runs regardless of whether the connected light switch is in the on or off position. The light switch needs to be switched into the 'on' position and left for several minutes for the in-fan switch to reset. It will then operate as it should. If the light switch is quickly turned on and off this won't work either (the fan will continue to run indefinitely). It needs several minutes in the light switch 'on' position to reset itself and can then be switched off and, after the run-on, will power off automatically.

The manufacturer (Envirovent) didn't suggest this either but it does now seem to be working!

Thanks again for your very kind and well informed help!

Barry.

Very good, glad you have it working.

Thanks for letting us know.

I've never come across that procedure so will bear it in mind for the future.
It's like PIR lights - good to know.

EFLImpudence said:

I've never come across that procedure so will bear it in mind for the future. It's like PIR lights - good to know.

Click to expand...

I also recently came across a timer fan which behaved like that and (not having read the MIs ) I was pulling my hair out for quite a while!

As you say, it's just like the behaviour which we are used to seeing with PIR lights - and I suppose the ability to over-ride the fan's timer and put it into a 'permanently on' mode would occasionally be useful. Maybe we are going to gradually see this sort of functionality become the norm with timer fans?

Kind Regards, John

JohnW2 said:

I suppose the ability to over-ride the fan's timer and put it into a 'permanently on' mode would occasionally be useful.

Click to expand...

I didn't think of that. It could be.