Boiler air pressure switch

Discussion in 'UK DIY' started by Pete Verdon, Nov 10, 2008.

  1. Pete Verdon

    Pete Verdon Guest

    Morning,

    Over the last few days, I've been getting an intermittent fault in my
    boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    "fan on but air pressure switch not activated", or words to that effect.
    Turning the power off and on again (can you tell I'm a software
    engineer? :) ) clears it for some hours / up to a day.

    I have the service manual for it, and can see that the air pressure
    switch and venturi (and the fan) is mounted inside the "sealed chamber"
    (but not in the combustion chamber itself). I'm satisfied with my
    competence to open this up (and in any case it's not actually
    gas-carrying) but I'm not sure what I'd do when I get there if nothing's
    obviously damaged.

    It seems to me that the switch is not necessarily the culprit - it could
    be doing its job perfectly and warning that the pressure is not changing
    due to some other fault. So I don't want to just order another switch
    and slap it in.

    Any suggestions on how to proceed?

    Cheers,

    Pete
     
    Pete Verdon, Nov 10, 2008
    #1
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  2. Pete Verdon

    BigWallop Guest

    "Pete Verdon" <> wrote in
    message news:49181f04$0$507$...
    > Morning,
    >
    > Over the last few days, I've been getting an intermittent fault in my
    > boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    > "fan on but air pressure switch not activated", or words to that effect.
    > Turning the power off and on again (can you tell I'm a software
    > engineer? :) ) clears it for some hours / up to a day.
    >
    > I have the service manual for it, and can see that the air pressure
    > switch and venturi (and the fan) is mounted inside the "sealed chamber"
    > (but not in the combustion chamber itself). I'm satisfied with my
    > competence to open this up (and in any case it's not actually
    > gas-carrying) but I'm not sure what I'd do when I get there if nothing's
    > obviously damaged.
    >
    > It seems to me that the switch is not necessarily the culprit - it could
    > be doing its job perfectly and warning that the pressure is not changing
    > due to some other fault. So I don't want to just order another switch
    > and slap it in.
    >
    > Any suggestions on how to proceed?
    >
    > Cheers,
    >
    > Pete
    >


    This type of thing can be caused by the change in weather, and having wind
    blow back into the flue and cause false detection. You say that a power
    cycle sometimes clears it, or is it coincidence that your power cycle
    coincided with a drop in the wind, or even the direction changed.

    For me, it's a difficult one to diagnose unless you are standing in front of
    it, I'm afraid. I hope other more knowledgeable souls come along with a few
    more suggestions for you to try.
     
    BigWallop, Nov 10, 2008
    #2
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  3. Pete Verdon

    Cicero Guest

    On Mon, 10 Nov 2008 11:46:12 +0000, Pete Verdon wrote:

    > Morning,
    >
    > Over the last few days, I've been getting an intermittent fault in my
    > boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    > "fan on but air pressure switch not activated", or words to that effect.
    > Turning the power off and on again (can you tell I'm a software
    > engineer? :) ) clears it for some hours / up to a day.
    >
    > I have the service manual for it, and can see that the air pressure
    > switch and venturi (and the fan) is mounted inside the "sealed chamber"
    > (but not in the combustion chamber itself). I'm satisfied with my
    > competence to open this up (and in any case it's not actually
    > gas-carrying) but I'm not sure what I'd do when I get there if nothing's
    > obviously damaged.
    >
    > It seems to me that the switch is not necessarily the culprit - it could
    > be doing its job perfectly and warning that the pressure is not changing
    > due to some other fault. So I don't want to just order another switch
    > and slap it in.
    >
    > Any suggestions on how to proceed?
    >
    > Cheers,
    >
    > Pete


    =========================================
    Blow through the air switch tubes - might be a bit clogged up with dust.
    It might not work but at least it can't do any harm.

    Cic.

    --
    ==========================================
    Using Ubuntu Linux
    Windows shown the door
    ==========================================
     
    Cicero, Nov 10, 2008
    #3
  4. Pete Verdon

    geoff Guest

    In message <49181f04$0$507$>, Pete Verdon
    <> writes
    >Morning,
    >
    >Over the last few days, I've been getting an intermittent fault in my
    >boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    >"fan on but air pressure switch not activated", or words to that
    >effect. Turning the power off and on again (can you tell I'm a software
    >engineer? :) ) clears it for some hours / up to a day.
    >
    >I have the service manual for it, and can see that the air pressure
    >switch and venturi (and the fan) is mounted inside the "sealed chamber"
    >(but not in the combustion chamber itself). I'm satisfied with my
    >competence to open this up (and in any case it's not actually
    >gas-carrying) but I'm not sure what I'd do when I get there if
    >nothing's obviously damaged.
    >
    >It seems to me that the switch is not necessarily the culprit - it
    >could be doing its job perfectly and warning that the pressure is not
    >changing due to some other fault. So I don't want to just order another
    >switch and slap it in.
    >
    >Any suggestions on how to proceed?
    >

    You could always check the APS

    Check the closed and open contact resistance - you want it to be in the
    region of an ohm or less, this involves checking your probe resistance
    first. You can activate the APS by GENTLY sucking or blowing on one of
    the rubber tubes to the APS. Kink the tube and leave it kinked for 30
    seconds or so to check that the APS membrane is not ruptured.Also check
    for a split or suchlike in the rubber tubes

    check the seals, check the flue,

    Are you experiencing the high winds we are getting around here ? If your
    flue is exposed, you might be getting blowback

    --
    geoff
     
    geoff, Nov 10, 2008
    #4
  5. Pete Verdon

    geoff Guest

    In message <>, Cicero
    <> writes
    >On Mon, 10 Nov 2008 11:46:12 +0000, Pete Verdon wrote:
    >
    >> Morning,
    >>
    >> Over the last few days, I've been getting an intermittent fault in my
    >> boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    >> "fan on but air pressure switch not activated", or words to that effect.
    >> Turning the power off and on again (can you tell I'm a software
    >> engineer? :) ) clears it for some hours / up to a day.
    >>
    >> I have the service manual for it, and can see that the air pressure
    >> switch and venturi (and the fan) is mounted inside the "sealed chamber"
    >> (but not in the combustion chamber itself). I'm satisfied with my
    >> competence to open this up (and in any case it's not actually
    >> gas-carrying) but I'm not sure what I'd do when I get there if nothing's
    >> obviously damaged.
    >>
    >> It seems to me that the switch is not necessarily the culprit - it could
    >> be doing its job perfectly and warning that the pressure is not changing
    >> due to some other fault. So I don't want to just order another switch
    >> and slap it in.
    >>
    >> Any suggestions on how to proceed?
    >>
    >> Cheers,
    >>
    >> Pete

    >
    >=========================================
    >Blow through the air switch tubes - might be a bit clogged up with dust.
    >It might not work but at least it can't do any harm.
    >

    Well yes it can

    you can rupture the APS diaphragm

    --
    geoff
     
    geoff, Nov 11, 2008
    #5
  6. Pete Verdon

    Cicero Guest

    On Tue, 11 Nov 2008 00:00:22 +0000, geoff wrote:

    > In message <>, Cicero
    > <> writes
    >>On Mon, 10 Nov 2008 11:46:12 +0000, Pete Verdon wrote:
    >>
    >>> Morning,
    >>>
    >>> Over the last few days, I've been getting an intermittent fault in my
    >>> boiler (a Chaffoteaux Brittony combi). The code it blinks translates to
    >>> "fan on but air pressure switch not activated", or words to that effect.
    >>> Turning the power off and on again (can you tell I'm a software
    >>> engineer? :) ) clears it for some hours / up to a day.
    >>>
    >>> I have the service manual for it, and can see that the air pressure
    >>> switch and venturi (and the fan) is mounted inside the "sealed chamber"
    >>> (but not in the combustion chamber itself). I'm satisfied with my
    >>> competence to open this up (and in any case it's not actually
    >>> gas-carrying) but I'm not sure what I'd do when I get there if nothing's
    >>> obviously damaged.
    >>>
    >>> It seems to me that the switch is not necessarily the culprit - it could
    >>> be doing its job perfectly and warning that the pressure is not changing
    >>> due to some other fault. So I don't want to just order another switch
    >>> and slap it in.
    >>>
    >>> Any suggestions on how to proceed?
    >>>
    >>> Cheers,
    >>>
    >>> Pete

    >>
    >>=========================================
    >>Blow through the air switch tubes - might be a bit clogged up with dust.
    >>It might not work but at least it can't do any harm.
    >>

    > Well yes it can
    >
    > you can rupture the APS diaphragm

    =========================================
    I meant *disconnected* tubes and should have said so because I wouldn't
    ever suggest blowing dust *into* any piece of equipment like a switch.
    Thanks for pointing out the possibility of damage to the switch and I
    should add the possibility of blow-back of dust into the blower's eyes.

    Cic.

    --
    ==========================================
    Using Ubuntu Linux
    Windows shown the door
    ==========================================
     
    Cicero, Nov 11, 2008
    #6
  7. Pete Verdon

    Pete Verdon Guest

    Cicero wrote:
    > On Tue, 11 Nov 2008 00:00:22 +0000, geoff wrote:
    >> Cicero <> writes


    >>> Blow through the air switch tubes - might be a bit clogged up with dust.
    >>> It might not work but at least it can't do any harm.


    >> Well yes it can
    >>
    >> you can rupture the APS diaphragm


    > I meant *disconnected* tubes and should have said so because I wouldn't
    > ever suggest blowing dust *into* any piece of equipment like a switch.


    It's a fair point - without the warning I quite likely would have blown
    through the valve body. I'd hope that I have sufficient mechanical
    sympathy not to rupture anything in the process though, unless these
    diaphragms are unusually sensitive.

    At the moment, I'm hoping it's just the wind direction as BigWallop and
    Geoff suggested :). It hasn't happened again since I posted.

    Pete
     
    Pete Verdon, Nov 12, 2008
    #7
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