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Bathroom extractor won't turn off

Discussion in 'Electrics UK' started by musashi79uk, 4 Apr 2020.

  1. musashi79uk

    musashi79uk

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    I had an extractor fan installed by an electrician when he did some other work in the house. It was an Awenta brand (not my choice but was included in the price of the other work) with timer and humidistat. I never liked the Awenta fan so I decided to replace it with an Xpelair one with just a timer.
    The Awenta was wired into the light switch outside the bathroom so would come on with the bathroom light. The wiring to the Awenta fan was Brown to Live, Grey to Neutral, Black to Timer and Earth sleeved and running inside the casing.
    I've disconnected those and wired them onto the Xpelair as Brown to Live, Grey to Neutral, Black to LS and Earth sleeved and running inside the casing. There is a dial inside the fan for the timer to adjust from 2 minutes to 32 minutes. I set that at just after 2.
    With the bathroom light switch off, I turn the fuse on from the CU. The fan doesn't come on. I turn the bathroom light on and the fan starts up. I turn the bathroom light off and the fan continues as expected as it has a timer but it doesn't stop after 2 minutes. It doesn't stop after 5 minutes. It doesn't stop after 8 hours. It's still spinning away.
    If I knock the fuse off in the CU, the fan stops. I turn the fuse on and the fan doesn't start back up until I turn the bathroom light on again, then it starts and won't turn off until I kill the power in the CU again.
    I've tried to change the grey and black the other way around. That way the fan goes on when the bathroom light is turns on but goes off as soon as you turn the light switch off. It won't even run on the timer.
    It's the Xpelair XS100T fan.

    Any help would be much appreciated.
     
  2. AndyPRK

    AndyPRK

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    What type of bathroom light do you have? Fillament,cfl,led ?
     
  3. EFLImpudence

    EFLImpudence

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    Timer faulty - not switching off.
     
  4. musashi79uk

    musashi79uk

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    It's a Philips Energy saving bulb.
    This is the 2nd fan I've out in. I bought the Xpelair one in January to replace the Awenta. Fitted it yesterday and experienced the issues I mentioned to I bought the same one from Toolstation this morning, fitted it and experienced the exact same problem with it not switching off.
     
  5. muffking

    muffking

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    Also you say -
    Brown is Live,
    Grey is Neutral
    Black is Switched Live

    But you then said you changed the grey and black the other way around. So you switched N & SL and it came on/off with the light?

    Are you able to get a multimeter and confirm which colours are L, SL & N?
     
  6. musashi79uk

    musashi79uk

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    Sorry, I meant I changed Brown and Black. Left Neutral how it was.
     
  7. musashi79uk

    musashi79uk

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    These are images of the wiring. 1 photo is the old fan before I disconnected it and the 2 are of the new (2nd) one I bought today.
     

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  8. flameport

    flameport

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    Switch the light off, switch the circuit off at the CU (so the fan stops)
    Remove the bulb, then switch on at the CU.
    Now switch the light on (fan should start but obviously no light), switch the light off and see if the fan stops after a few minutes.
     
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  10. musashi79uk

    musashi79uk

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    Excellent! That did the job. Was it the bulb it didn't like?
     

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  11. Chris_W

    Chris_W

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    Post answered.
     
  12. securespark

    securespark

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    Must be, but I haven't seen that before.
     
  13. EFLImpudence

    EFLImpudence

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    Nor me. Could someone explain it?
     
  14. securespark

    securespark

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    All heads turn to Mr F Port.....
     
  15. AndyPRK

    AndyPRK

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    try fitting a old lamp or LED and check the timer function still works
     
  16. flameport

    flameport

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    With the fan running, there is a connection between L and SL of a certain resistance due to the internal circuitry of the fan timer.
    With the fan not running, that resistance is either not there, or is sufficiently high that the following effects don't occur.

    With the light switch on, both L and SL at the fan are connected to the same 230V. The fan timer is triggered continuously so the fan starts and stays on.

    With the light switch off, L is still connected to 230V so the fan keeps running.
    What SL is connected to and what happens next depends on the lamp installed:

    1. Filament lamp installed:
    A tiny current flows from L to SL in the fan, through the low resistance lamp filament and to neutral.
    Result - voltage on SL is zero. The timer is not triggered and the fan stops after the preset time has elapsed.

    2. No lamp installed:
    No current can flow from L to SL, so the voltage on SL depends entirely on the internal resistance of the fan timer between L and SL. The timer is designed so that this is lower than the trigger threshold of the timer, so the fan stops after the preset time has elapsed.

    3. CFL that causes the problem installed:
    This will have a capacitor inside between L&N (plus various other components)
    A tiny current flows from SL and charges the capacitor in the lamp, this causes the voltage on SL to rise gradually.
    If the capacitor charge time is less than the time set on the fan, the voltage across the capacitor (and therefore on the fan SL terminal) will rise to a level sufficient to trigger the timer in the fan, which resets the timer and the fan keeps running.
    Eventually the capacitor will discharge when the CFL tube conducts, this may be seen as a visible flash in some cases.
    The cycle then repeats, with the capacitor charging again and resetting the timer in the fan.

    This is related to the problem of certain CFLs flashing intermittently when off, or some LEDs glowing dimly, although in this case it only occurs if the fan has already started as the source of the current is the fan itself.
     
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