baxi boiler pressure gauge problem.

Discussion in 'Plumbing and Central Heating' started by 32tybeams, 18 Oct 2011.

  1. 32tybeams

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    I have a baxi combi 80e boiler. I'm finding that every morning i have to check the pressure gauge. The needle always seems to drop to 0.5. Being in fear of it droping to under that. I then refill using the filling loop Only reilling upto 1 notch above: 0.5. Then a few hours later when i switch heating on ( the needle being in the same place as was after refilling earlier) the needle gradually goes up to 3. Then gradually drops down to where it should be normally. Anybody have any idea why this is happening? And what i should do about it?
     
  2. misterdubya

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    Look up FAQ's.

    Expansion Vessel flat or knackered.
     
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  3. MANDATE

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    When water gets heated it expands in volume. The extra water has to be accommodated using an expansion vessel. The vessel has a flexible diaphragm which is initially held to one side by inflating the other side with air
    In operation the heated water will push against the diaphragm and compress the 'air' which will be released again when water cools down.
    It is suggested that over time the initial 'air' pressure has been lost or greatly reduced. This has resulted in too small a volume for the extra water and in turn the water pressure rises. There is a relief valve set to open and discharge water at 3bar pressure and when it does this the 3bar pressure is released and the PRV quickly closes again leaving a pressure of 0.5bar
    Sometime the PRV does not close properly, because of dirt on the seating face and it may have to be changed. It is important however to deal with the expansion vessel first.
    There is also a possibility the diaphragm in the expansion vessel is ruptured which would allow water to pass across to the 'air' side.
     
  4. 32tybeams

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    Thanks to your response. I'm getting the idea of problem now through reading and rereading it a few times as well as looking at the manual and identifying the mentioned parts. you seem to be very clued up about it. I will shop around and try to get a reasonable quote for inspection, repair or replace of the extention vessel and prv. I don't suppose you would have any idea what the cost is likely to be? Thanks again for being so helpful.
     
  5. MANDATE

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    I suggest you read the problem of 'AndyMcG' who has just resolved a similar type problem without bring in a heating engineer.
    From what I recall I think PRVs will be around the £15 mark and expansion vessels obvious vary according to size and make, I think I've seen some at 'Toolstation' around the £30 mark.
    However I think your problem is another case of the vessel losing air which results in the water pressure increasing to a unacceptable figure and opening the PRV.
    If you have a 'air pressure gauge' and bicycle/ car foot pump and follow the correct procedure you could do it yourself
     
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