Useful Repair Info...omnivent And Thetford.

Discussion in 'Motorhome Chat' started by pappajohn, Jul 6, 2015.

  1. pappajohn

    pappajohn Funster Life Member

    Aug 26, 2007
    YO11 2BD
    During our shakedown weekend away i fould the thetford toilet didnt flush (electric flush) and the Onmivent extractor was weak and intermittant.

    The toilet is a Thetford 200CWE.
    I replaced the fuse which blew the instant the flush button was pressed.

    The flush button is on a removable bezel which is held by two plastic 'posts' and some non setting mastic sealer...prise off carefully with a broad blade screwdriver.
    underneath the bezel is a plastic grid held with 4 screws...2 x rear..2 x front...ignore the center ones, they hold the plastic posts.
    when removed look to the left, you will see the white filter, follow the pipe down and you will find the pump.
    CAREFULLY unclip the pump amd hoses, one hose directly below the filter and one at the opposite side to the bowl outlet.
    lift out the pump, filter and hoses.

    Look underneath the pump, you will see a red wheel with ribs...this is the impellor and chances are it wont turn.
    use a small screwdriver to gently turn the impellor, it gets easier as you turn it.
    i stood it in a small glass of vinegar for half an hour to break up any limescale...seemed to help.

    Once it turns freely replace the blown fuse.
    its a 3amp but not having one i fitted a 5amp.
    hold a bit of rag over the pump outlet and press the flush button.

    If the fuse still blows you either have a duff pump or a wiring fault assuming the impellor is free to spin.
    reassemble in reverse order.

    The 3 speed reversible Omnivent. (Probably other models apply)

    The #1 common fault.....stuck brushes in the motor.

    Indoors, remove the 4 screws holding the fly screen and remove screen.
    remove motor wires from switch (theres only two and may be a resistor between them, do not seperate) taking note which goes where.
    the connectors are hard to get out of the small hole in the plastic motor mounting frame so i cut them and fitted new connectors on reassembly
    Hold the fan blades and remove the spindle nut, its threadlocked and tight, undo anticlockwise.
    remove the fan but MAKE A NOTE OF SPACER WASHERS !!! Inc the very thin nylon/fibre one.
    In my haste I think i got it wrong as on assembly the fan wouldnt turn.
    on the roof remove the 2 motor retaining screws and lift out the motor.

    using a thin driver seperate the top cover from the motor body, the driver may need a tap with a small hammer etc to start it moving.
    its hard to seperate as the permenant magnet tries to hold the cover on.
    in the cover are the will be stuck in its housing.
    dont attempt to remove either as the wires need desoldering first.
    i simply worked the stuck brush in and out in its housing until it moved freely.
    i also used some fine wet n dry paper to clean the commutator segments which, because of the stuck brush, has burnt slightly.
    reassembly is the reverse ensuring the brushes dont get trapped as the lid goes back on.
    i used a new nyloc nut on the spindle instead of the plain nut and threadlock.
    check the fan spins freely, if not you need to slacken the nut slightly...but only enough to allow the fan to spin....this may be where i got the spacers wrong.

    Start the fan on 1, then increase to 2 then 3.

    Speed 3 is now hurricane force and the fan whines slightly with the speed.
    the volume of air being drawn in or out is amazing compared to the feeble effort before.
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