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Boiler pressure drops to 1 bar each day

Discussion in 'Plumbing and Central Heating' started by Gecko207, 5 Jan 2004.

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

  1. Gecko207

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    I have a potterton puma combi bolier. The pressure in the bolier drops off to its lowest pressure eveytime i use the bolier, after about 3 hours of use.

    Can anyone help me to solve this problem? Does anyone know what is probably making this happen and how can I solve it?

    Cheers for all your help!
     
  2. sterose

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    For a start, does it just drop to 1bar, or does the boiler stop working at 1bar?

    Secondly, do you keep refilling it?

    Thirdly, do you know where the water is going (ie. Pressure Relief, or Leaks)?
     
  3. Gecko207

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    When the bolier pressure reaches 1 bar, the boiler stops working, i.e. both the hot water and central heating are lost. At the moment, when the pressure drops off, I have to open a valve to re-increase the pressure. I have been told that the boiler operates at about 1.2bar, so I re-increase it to about that level.

    But I don't refill it. Should I, and if so how do I that?

    There is a small leak on the boiler, but i was unable to trace the source of the leak. It probably loses an egg cup amount per week. It doesn't appear to be coming from any of the pipes, which are below the boiler, so I though maybe it was coming directly from the main part of the boiler. But I can't actually see from where.

    Thanks for responsing to my question!
     
  4. sterose

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    'Re-increase'? Do you mean refill.
    I.e. do you put water into the system, or do you just turn the pressure dial with your fingers... [joke]


    Assuming that my previous comment was humour, what do you do to 're-increase' the pressure.


    How do you know there is a leak then if you cant trace it?
    Or do you mean that there is a dripping from the boiler, but you don't know where it comes from?

    In any case, if your boiler is leaking internally, it is possible, depending on where the leak is, that most of the leaking water is being burned off (i.e. evaporated) by the heat, which is why your system loses .2bar while only 'leaking' an eggcup amount.
    What i'm trying to say, is that it must be leaking gallons to lose that much pressuse, but most of the leaked water is being evaporated by heat before it leaks out of the boiler.
     
  5. Gecko207

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    I guess I am refilling it when I repressurise it. When I open the valve below the boiler, I must be repressurising the boiler with water. I just watch the pressure gauge change as I open the valve, until it reaches the 1.2 bar.

    In terms of the eggcup worth of water....I find water on the inside base of the outer casing of the boiler. But when I've looked around the inner piping, and main boiler, within the outer casing, I can't find a source of the leak, i can't find where it is dripping from.

    So maybe the leak is the only source of the pressure drop? Or could it be something else?
     
  6. MANDATE

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    I agree your leak is the source of the pressure drop,
    If you imagine a expansion vessel containing a flexible rubber diaphragm with water on one side and air on the other side.
    Now you have to remember you can compress air but not water and also the pressure on each side of the diaphragm is equal.
    When you increase the pressure of water by 0.2bar you are adding a small amount of water so the volume of water increases and moves the diaphragm which in turn compresses the air on the other side until the pressures are equal. When your water gets hot it expands in volume and causes the air to be compressed a little more so the pressure increases a little further.
    In reverse order the pressure drops as the water cools down and also if you lose any water due to a leak the pressure will drop.
    You do not need to lose much water for the pressure to drop 0.2 bar and it cannot be gallons as suggested, I'll bet the total volume of water in the radiators, pipes and boiler only amount to a few gallons.
    So when the pressure drops to 1.0 bar it is not empty so it only wants the pressure increasing, not re filling.
    :rolleyes: :rolleyes: :rolleyes:
     
  7. Gecko207

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    Cheers Sterose and Mandate for your help!!!

    I guess now I need someone to come and check where the leak is coming from.

    Thanks again!
     
  8. sterose

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    "it cannot be gallons as suggested"
    Exageration.

    But it still takes a bit of water for it to drop .2bar consistently.

    Either way, try putting water up to 1.3bar and see if it still drops.

    "So when the pressure drops to 1.0 bar it is not empty so it only wants the pressure increasing, not re filling"
    You make no sense here.
     
  9. MANDATE

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    The point I was trying to make was that whilst there is a pressure of 1 bar present, the system is basically full, although to increase the pressure you have to increase the volume slightly and put back what small amount of water has been lost.
    :rolleyes: :rolleyes: :rolleyes:
     
  10. ChrisR

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    Look hard at the pressure relief pipe which might be dripping. It goes from the valve inside which has the red knob, on the right, usually straight through the wall. These quite often leak a bit, though when the water is warm it evaporates quickly so you dont see much.

    The ither thing to check is at the top of the boiler on the left, brass cylindrical thing which is an automatic air vent. This means water dripping down the lh side. The other place which often leaks on these is a temp sensor on a pipe inside lower right, which drips onto the pump.

    You'll have to tak e the front off to have a decent look - just a couple of screws under the outside edges then the front comes out up and off.

    Get it sorted. Taking in fresh water all the time is a seriously undesirable for the health of the boiler.

    Yet another place to look is at the isolation valves under the boiler - one each red and blue levers. DO NOT touch them! They will leak if you attempt to use them! "Engineers" will often turn them in order to isolate then empty the boiler of water. Bad idea - use a drain cock somewhere else on the system.
     
  11. david1

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  12. david1

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    Did you solve your problem with your boiler - I have aexctly teh same bolier and the same keeps hapening. The plumber changed the pressure relief valve yesterday as that was dripping but it seems to be getting worse.

     
  13. seanwosere

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    I have a similar problem...Pressure loss. There are no signs of leakage on any of the surface pipework, yet we were loosing pressure ie. going below 1 bar in about 5 hours. This all happened out of the blue one day. We had not been doing any works to the flat, or to the system, so it is not a leak that has been caused by damaging a pipe.

    70% of the pipework is underground and set in concrete, below a waterproof finish. At the moment we are assuming that this is where the leak is. We decided that as no water was coming back up or showing on the floor, and was dissipating into the soil below, it might be easier to change the pressurised system to a normally vented system and let this top itself up...to hell with the leak, let it drip!

    Well that didn't work! We now have the system sucking in enormous amounts of air to the point that some of the radiators will not even heat up....and in about 3 hours!

    The last thing we want to do is start digging up the floor, we have checked all surface fittings and pipes and found no leeks. Any suggestions would be greatly appreciated.
     
  14. david1

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  15. ftgpmb

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    We had the same problem on our Potterton Puma 100. Have had the expansion vessle changed to cure what we thought was a ruptured membrane. Problem was the plumber used the pressure releif valve to drain the boiler down so then the problem only got worse (i.e. water leaking through the PRV after refilling) After that was changed, things improved, but there is still a very slow leak (~0.2 bar per week) which means I have to keep topping it up (not good for corrosion as others have pointed out)

    But today, I think I have traced the problem to the automatic air vent. There seems to be water oozing out of the little black cap at the top. I can see where it has been evaporating inside the casing (hence no dripping out the bottom). All the instructions say you should leave the little black cap loose, but if there is water coming out .....

    does anyone know what the automatic air vent actually does and why it has to be left open? how do you know if it is broken?
     

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