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Why does pressurised system need bleeding often?

Discussion in 'Plumbing and Central Heating' started by reg091, 25 Feb 2016.

  1. reg091

    reg091

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    Pressurised CH system and I find that I need to bleed a fairly considerable amount of air from the towel rail (highest point) at least once a month.

    Each time I do that I then open the water inlets to put a bit more water in the system. Today I bled the air and noticed that there was very little water in the system at all (pressure gauge on boiler).

    Is it simply that there is a leak somewhere?

    I can't understand how a sealed system can lose water/get air in it.
     
  2. Hugh Jaleak

    Hugh Jaleak

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    May not be air, have you got the correct level (or any!) inhibitor in the system? An untreated system will be prone to electrolytic corrosion, which will create black sludge and hydrogen, which is often mistaken for air. If you've bled a lot of gas or air out, then the remaining water in the system will fill this space and pressure will drop.

    Its possible water has escaped slowly elsewhere over time, (these systems can and do leak!), hence the problems you are experiencing.
     
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  4. reg091

    reg091

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    Interesting, didn't know about hydrogen. Boiler only installed 2 years ago and system drained and inhibitor added then. I understand the principle that if I let gas (air/hydrogen) out of the system then I have to replace it with water, but I am mostly puzzled as to why once I have bled all the gas and topped it up with water I then have to keep doing it again regularly.
     
  5. Hugh Jaleak

    Hugh Jaleak

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    The corrosion would be a constant process, so gas would be slowly building up over time. Each time you top up the inhibitor level is being reduced slightly. How much would you consider as 'considerable'?

    Alternatively there could be a small leak somewhere allowing water to escape, and under certain conditions, air may be being drawn back in.
     
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