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Worcester Bosch 28i leak from Auto Air Valve

Discussion in 'Plumbing and Central Heating' started by Basher Walls, 6 Aug 2005.

  1. Basher Walls

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    Hi,

    I am experiencing a leak from my Worcester Bosch 28i Boiler.
    Upon inspection the leak is coming from the Auto Air Valve.
    I am not a plumber so I won't be trying to repair it, I am just trying to find some information about what caused the leak.
    The Boiler has been fitted for about 2 years and every now and again I had to top up the pressure from the filling loop.
    The Central heating hasn't been used in a while but the Hot water is used daily.
    I notice today that the Pressure is at 0 and the boiler is leaking.
    I have taken off the covers to find the cause and I can see water is dripping from the Air release valve - must have been a little while as there is a residue around the area.

    I have left a phone message with my plumber, but don't expect a return call until monday. I have also contacted Worcester Bosch and they have quoted £175 for replacement (standard Fixed Charge).

    I asked about the price of the part but as I am not an engineer/Installer they would not tell me.

    So, could anyone give me some more info on the Auto Air Valve, what could have caused the leak and approx how much they cost for the part.

    I would like to know a little more information on the problem if possible.

    Thanks in advance.


    Edit - I managed to talk to a mate who is a Ex plumber and he has given me some info.

    It seems that limescale has built up around the valve part and this caused the jam. Once jammed whilst open the water ebbs out from the top.
    He was quite surprised that the Valve would have that extent of Scale in two years, but he says that it can happen. Changing the valve is the best option as repairs to them are quick fixes.
    He has suggested tapping the side of the valve a few times to see if it will release the ball within the valve (which has jammed).
    Just done that and it works - leak fixed.

    My mate says that this is only a quick fix and it would be best to replace the part to save any more hassle.

    I am happy with that but if anyone has an idea on - cost of part approx and some more info on how it happened, please let me know.
     
  2. chrishutt

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    Leaking AAVs are very common on combi type boilers. Seems to be some basic design fault with valves, otherwise it wouldn't be so common! Anyway we just have to live with it, and as you have been advised, it is not generally worth trying to clean an old AAV.

    Many combi boilers will take a standard AAV with a 3/8" male thread. These are available for about £3 (e.g. from BES). Easy to fit (having isolated and drained boiler), unscrew old, screw in new.

    However some boilers require an AAV with a unique connection, in which case you need the official spare part - likely to cost more than £10. But fitting usually easy, same principle as above.

    Refer to the manufacturers instructions for your boiler. At the back will be a short list of spare parts which will include the AAV. You should be able to see what sort of connection it has.
     
  3. ollski

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    In the meantime to stop the leak just shut the cap down and release it as and when to bleed it like a manual valve.
     
  4. Basher Walls

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    Thanks,

    I would screw in the cap - except mine is missing.
    Upon reading the instructions it advises you to remove it.
    Oh well.

    My Plumber has contacted me and has arranged a date of the 18th Aug.
    If he gets some spare time beforehand then he will call earlier.
    I know it is still leaking, but very slight now after the 'tapping fix' and I am confident it will last 2 weeks.

    I expect the part to be more expensive but I don't know how to drain the system and de-pressurise the boiler.
    I will just have to wait, even though this is a easy fix.

    Thanks again.
     
  5. Paul Barker

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    Well manufacturers have put a very convenient drain off, officially known as a Pressure Release Valve (isolate flow and return pipes <biggest two which get hot when heating has been on a while> turn red button and hold 1/4 turn where it has drawn most towards until sound of water scalding cat outside stops). The bad news though is that if you use that IT will probably start to leak too, if it hasn't already (if it leaks get heating real hot and let a gusher out of it crossing toes and fingers that this will work or you have now got to change that part aswell). Some manufacturers provide a genuine drain off on the boiler. If not safest option is to use the drain off in the system and drain it down below the boiler and refill afterwards. Loosten air vents on rads when draining so water all drains out of them so as not to cause air locks when refilling.

    When replacing the auto air vent (which is like a carbureter <look I can't spell and don't care about it> float valve) mostlky they have a rubber o ring seal lubricate that with spit when assembling so it doesn't get pinched. If there isn't one or you are using a generic one, copious amounts of ptfe tape does an excellent job.

    I wander if a tyre valve dust cap fits?
     
  6. ChrisR

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    I would say you don't need to drain the rads - so leave the vents shut and maybe only 1 will need bleeding afterwards, the rest keep their water. Close rad valve one end if you like.

    SOmebody else will do it a different way ...!
     
  7. Basher Walls

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    I will probably leave it until the Plumber arrives.
    I wouldn't want to damage the boiler any more than it is!

    The boiler has Isolation valves on the two pipes and a pressure release valve which leads to a pipe situated outside.

    My guess is that I would lock down the two pipes at isolation one feed and one return. Once done open the pressure release valve and the water will run outside - Close Pressure valve once complete.
    Now empty, the AAV can be swapped over and the seal may require a new one.
    Release/remove the 'Dust cap' and then turn on the feed and then the return Isolation valves.
    Once completed the rads can be bled.

    I am pretty sure that it would work, but is it worth risking a £500 - £600 boiler for something that is cheapish to fix.

    Thanks anyway - It would be nice for someone to confirm my guess though! :confused:
     
  8. chrishutt

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    Perfecto Basher.

    Just add that you would have to restore system pressure (to 1 bar min) using the filling loop......Go on, have a go?
     
  9. bradleybear

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    From personal experience, a word of advice.

    1) Don't go anywhere near the flow/return isolation valves, these will leak and cause you an even bigger headache.

    2) Likewise leave the Pressure relief valve alone, as these often fail to shut off, and will need cleaning, replacement of rubber.

    Ok, so find a drain off point on your central heating, now attach a hose, lead to a drain/outside, and open the drain off until pressure is released (pressure gauge at zero on boiler). Decision time, change the auto air vent, or change the internals. Either one can be done quite easily. This might puzzle a few old pro's, but it is far easier to change the internals of an auto air vent than to change the complte valve itself. Worcester air vents are a Caleffi vent, so simply support the body, and unscrew the top section of the air vent (the large knurled top piece). Once unscrewed, simply change for the new internals of the new air vent.
    Auto air vents have a small plastic float inside connected to a plastic arm, once removed, just a brass body is left behind. Normal points of failure is dirt inside and they fail to seat properly. This removal of the internals removes the chance of leakage on the 3/8" or 1/2" o-ring at the base.
    This is a very useful method of dealing with Worcester Cdi range air vents, when it is sometimes awkward to remove the valve from the section of pipe on top of the heat exchanger.
    Once air vent repaired, close drain off point, and refill heating circuit to normal system pressure.
     
  10. Paul Barker

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    Yes I'd forgotten older isolation valves are also prone to leak if operated. A very good point.

    Some boilers you're scared to touch anything at all because you start off a chain of events that result in four problems as well as your original one.

    Last time I had to have Worcester man out to a Buderus I was trying to make conversation with im, so brought up the good old 240 combi with natural draft, expecting him to go all glassy eyed. He said "we won't touch anything over 10 years old". Quite sensible, very nice to be able to take that stance, but we have to offer a better service than that. I now prefix any work on such a boiler with that story and tell the customer I'm starting workat their risk not mine.
     
  11. Basher Walls

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    My Worcester Bosch 28i is Two years old so I was slightly surprised that the AAV was damaged already. That said I always had slight drops in pressure. I have noticed that the residue on the pipes leading down from the AAV make me think that it has been Leaking slightly for a While - maybe since it was Fitted!!

    As for it now - Back to normal, no actual leaks dripping but a small bobble of water at the AAV. That could be how it has been for a long while.
    I am getting it replaced later in the month, so I am continuing with getting the plumber to do it as it should be done - it will only get worse.
     
  12. bradleybear

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    Worth a mention, but if the isolation valves ever leak on most boilers, a dose of Leak Sealer injected through the filling loop 99/100 will fix the leak. Lost count how many times I've done it now. It sure gets you out of trouble on a Friday afternoon! (sentinel is the one I use, cartridge format)
     
  13. Paul Barker

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    Thanks for that tip.
     

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