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Boiler pressure dropping

Discussion in 'Plumbing and Central Heating' started by Katade, 22 Aug 2003.

This topic originated from the How to page called Problems associated with noises from the central heating system.

  1. Katade

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    The boiler in my house (Valliant) was inherited from the previous owner, hence no instructions. I have to keep on opening a valve to underneath the boiler to increase the pressure as it keeps dropping below the red line (just below 1 bar). The other day I forgot the switch the valve off and the pressure went above 3bar and the overflow was dripping (which was good), but within 3 days the pressure was below the marker. Surley this can't be right. I should not need to keep on topping up the system every week or so, should I? What could be wrong?

    PS - I can't see any leaks in the house and all the rads are okay.
     
  2. breezer

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    sorry to state the obvious but you do have a leak somewhere. If its of any use I had the exact same problem, turned out that the drain valve (under the ground floor) was not tight, we are talking 1 drip /10 minutes but over time it was enough to cause the pressure to drop
     
  3. Tin Gill

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    I had a similar problem with my Vaillant combi and it turned out to be the pressure valve for the overflow that had begun to stick and so never shut properly. You mentioned that when the pressure went above 3 bar the overflow was dripping - you might want to check it's not dripping all the time.
     
  4. Gees

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    I still have a leak somewhere.. It takes about 3 weeks to drop by abt. 1/10 of a bar. can I find it? Can I H**L.
     
  5. COG

    COG

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    Anything much more than 1/2 a bar over three months is too much, every time you top it up your adding fresh water which means more oxygen which means more corrosion. Dont expect to see a puddle of water from it is more likly a trickle from a rad valve or the PRV passing
     
  6. ChrisR

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    You won't find a leak that small probably, they tend to evaporate straight away. I'd add Leak Sealer - get it in a plumbers merchant and ask them how to get it in the system .
     
  7. corgiman

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    my opinion is that when the system over pressurised the Pressure relief valve opened, quite correctly, but has not closed off properly. In my experiance this is due to a bit of muck in the seating and the sealing washer has corroded and needs replacing

    If the pressure drop never happened before then a system leak is unlikely but it won't hurt to put some leak sealer in as ChrisR suggests
     
  8. corgiman

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    I think the problem is that when the system over presuurised the Pressure Relief Valve opened, quite rightly, but has failed to close off correctly due to a bit of muck or the sealing washer being corroded.

    if the drop never happened before then a system leak is very unlikely but it won't hurt to inject some leak sealer in as ChrisR suggests
     
  9. pb

    pb

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    I have a similar problem but cannot find any visible leak site. Does anyone have any views on one possible explantion:-

    There is at least one location where a leak would not be visible/obvious. If general hot water tank (HWT) is also heated by the boiler CH circuit then there could be a leak in the loop passing through the HWT. The direction of leak would of course be from hi to lo pressure. Thus, if the CH circuit is at higher pressure than HWT then water will leak (unseen) into the hot water tank until p difference is zero.

    A clue as to whether this explanation is valid would be to check the pressure to which the boiler CH circuit levels out to following topping-up from main. If that roughly equates to the pressure head in the HWT circuit then maybe the leak is within the CH circuit where it passes through the HWT. One bar of pressure is approx equivalent to 30 foot head of water.

    Incidentally, does any one know why the Vaillant Instruction Manual warns that " No inhibitors must be added to the C.H. system"? Surely that would only be tenable for the ideal situation of a system that is perfectly sealed and thus the supply of oxygen limited?
     
  10. jcb

    jcb

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    I am also having a problem with a pressure drop about .2bar per day, it is coming from the pressure release valve. Is it just a matter of replacing the valve or could there be another cause???
     
  11. Galileo2004

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    Same problems here with my Worcester Heat Systems Combi. I have now turned off all the radiators (valves off at both ends), put more water in so that the pressure returns to 1bar and will wait to see if the pressure drops back to zero again (which normally takes 2-3 days).

    The pressure release valve may be dripping, but its hard to determine when its raining outside.

    Does anyone have any other suggestions on where to find the leak?
     
  12. murphytanya

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    The pressure at my boiler drops below 1 bar (it takes about 2 weeks to drop to 1/2 bar). I do see a visible leak at the top of the expansion tank that is hooked up to the boiler. Would a leak in this location be causing the pressure drop? I was told by a plumber that it would not, since the flow of water from the boiler to the radiant heat system doesn't pass by the expansion tank. Any thoughts?
     
  13. buck51

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    Why do you think, pb, jcb, & Galileo2004, did not get a response???
    Start your own post this one died twice 2003 & 2004 then you may get a beter response than they did.
     
  14. findaleak

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    Hi Everyone

    If you have leaks you cannot locate, check out findaleak.co.uk they are the central heating leak gurus !!

    Cheers
     
  15. corgiman

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    spam spam spam

    wonderful spam

    :)
     

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