Boiler Pressure worry

Discussion in 'Plumbers' Talk' started by Boiler pressure worry!, Jan 9, 2010.

  1. I have a question I hope someone can help me with about the water pressure on my Vaillant combi boiler. When I moved in, the owners left a note saying I should keep the pressure gauge at 1 by adjusting the water in the system using the two screws under the boiler. At this point I noticed the pressure was at about 1/2 - so I topped it up to 1.
    This was when the boiler was off/cold.
    When I put the heating on, after a few hours the pressure gauge was up at 3/at the red line!
    I turned off the boiler and when it cooled, bled some water out of a radiator.
    What I find is that if I top the system up to 1 then when I switch the heating on, the gauge goes up to 3 but if I top it up to 3/4 then the gauge will settle at about 2,1/2 when on.
    However, it always seems to drop down from 3/4 to 1/4 (sometimes overnight) and I find I'm topping it up most days.
    Should I just continue like this or is it okay to let the boiler run at 3 when the heating is on. All I can find on the internet is advise to top it up to 1 when the boiler is cold - I can't find anything on what the safe pressure is when the boiler is running - any advice would be greatly appreciated.
     
  2. Cornish

    Cornish New Member

    The good news is its safe.
    The bad news is its not good.
    Topping the boiler up every day is never a good this.
    If I was doing long distance diagnosis I would suggest the expansion vessel is no longer at the required pressure, it may just need pumping up or at worst replacing.
     
  3. dav0

    dav0 New Member

    Had this problem with my boiler ( vaialnt gbh 282e combi compact ) turned out to be the pressure vessel that was de-pressurised.Shut off both f&r and opened the relief valves on the f&r outlets nearest the boiler.when i repressurised ( the pressure vessel ) black filthy water was expelled from the relief valves!!had to keep re-pressurising the vessel until water stopped flowing ( about 10-15 minuets ) finally checked pressure vessel to 1 bar and system now runs sweetly.I assume water enetred the vessel due to ther being no pressure there, if you are unsure at all about what to do then get an engineer in as the pressure vessel should not be over pressured.
     
  4. JLX90

    JLX90 New Member

    Also you probably have a leak in the system somewhere if the pressure drops below what you origanaly pressureised it to when cold, It could be the discharge valve letting by seeing as your pressure has been to max that's my bet.
     
  5. Thanks very much for the help.
    The heating seems to still work fine even at 1/2 on the gauge - will using it at this pressure damage the boiler?
    If I increase the pressure to 1 in the system, (strangely it doesn't drop back down at this level - only when it's below 1!) is it safe to use if the pressure goes up to 3, and in the red, when the heating is switched on?
    I can find lots of internet sites that say the minimum pressure when the system is switched off is 1 but I can't find out what the maximum safe pressure is when the system is switched on.
    What's the safe limit that the pressure should increase by between switched off and switched on?
     
  6. joinerjohn

    joinerjohn New Member

    the pressure in your system when cold will always be lower than when the boiler is running. Water expands when its heated. It's quite normal for the pressure to rise when it's running. If your losing pressure, I reckon the first thing to check is the pressure relief valve (PRV) If this has opened to let excess pressure out then it could have some carp stuck in it preventing it from closing properly.
     
  7. Thanks joinerjohn.
    Is an increase from 1 to 3 netween on and off acceptable/normal?
    I'll get it checked over when the weather improves but I can save myself the daily system top-ups if I increase the cold pressure to 1 - it only seems to lose pressure when the gauge is already below 1.
    But do I risk damaging it by setting it to 1 and then having the hot/ON pressure go up to 3?
     
  8. dav0

    dav0 New Member

    Pressure should rise between 1.5 to 2.0 bar depending on the boiler stat setting ( at 70-80 degrees pressure should be about 1.5 bar ) the pressure vessel need repressurising to about 1 bar, if you don't know how to do this get somebody in to do it for you!!!!
     

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