Closed CH system - ? low pressure

Discussion in 'Plumbing and Central Heating' started by swayzak, 11 Dec 2019.

  1. swayzak

    swayzak

    Joined:
    1 May 2008
    Messages:
    98
    Thanks Received:
    0
    Location:
    Leicestershire
    Country:
    United Kingdom
    Hello

    We recently had the CH system in our (large-ish) old Victorian house converted from open to closed system.

    I have noticed that the pressure gauge (next to small red metal tank which was added as part of change) often falls below red warning needle (set at 1 bar) when heating is off.

    When heating is on the gauge reads between 1 and 2 bar.

    Is this normal ?

    We regularly get air in one particular radiator on ground floor, (immediately above the boilers - these are in cellar), so this needs bleeding quite often. This issue pre-dates the change over to closed system.

    Are the 2 issues connected ? If so what can be done to fix this ?

    One plumber suggested putting in something to fill leaks and then possibly a power flush to remove corrosion / sludge.

    There are no obvious external signs of leak in the CH system.


    Thanks
     
  2. Sponsored Links
  3. Gasguru

    Gasguru

    Joined:
    9 Sep 2005
    Messages:
    12,714
    Thanks Received:
    3,435
    Location:
    Sussex
    Country:
    United Kingdom
    For a typical property the pressure should be set to 1 bar with the radiators cold.
    The pressure will rise during heating due to water expansion...ideally the pressure should not rise to more than 2 bar when the radiators are all hot...1.5 would be better.

    The pressure drop and the continuing trapped air issue indicates a likely leak on the system and needs attention.

    I would not suggest a powerflush unless there are known flow issues...you are more likely to cause problems (there's always a chance it will create leaks) and it's often suggested due to it being a good earner.
    There are chemical leak sealers to inject into the system but they are a last resort...there's no guarantee they will work and they could invalidate your boiler warranty.
    Find the leak is the best option...starting with radiator valve spindles etc.
     
    • Like Like x 1
  4. swayzak

    swayzak

    Joined:
    1 May 2008
    Messages:
    98
    Thanks Received:
    0
    Location:
    Leicestershire
    Country:
    United Kingdom
    Thanks

    There is some evidence of leak around some of the old radiator valves (green stain) but nothing active I can see. Would this be enough to half fill a radiator every few weeks or so ?

    Some of the radiators are pretty old (lovely though) so may be internally created gas/air ? If so how an earth do you track this down to fix it ?
     
  5. ianmcd

    ianmcd

    Joined:
    15 Aug 2010
    Messages:
    24,915
    Thanks Received:
    10,885
    Location:
    Livingston
    Country:
    United Kingdom
    you say that you are reg bleeding some radiators, after you bleed any radiator you have to top the pressure back up, swapping an open vent system to a sealed system always run the risk of small weeps
     
  6. Gasguru

    Gasguru

    Joined:
    9 Sep 2005
    Messages:
    12,714
    Thanks Received:
    3,435
    Location:
    Sussex
    Country:
    United Kingdom
    Leak under floor maybe?
    I've had several customers with one particular rad collecting air and requiring regular bleeding....it's always been down to a leak bizarre as it sounds given it's a presurised system.
     
  7. oldbuffer

    oldbuffer

    Joined:
    6 May 2010
    Messages:
    1,594
    Thanks Received:
    598
    Location:
    London
    Country:
    United Kingdom
    How many radiators and what type. If lots and they are the "school" type, they hold a large volume of water. The expansion vessel needs to be sized to hold 4% of the total volume of water in the system without going over pressure. What size expansion vessel (litres) do you have?
     
  8. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
  9. Sponsored Links
Loading...

Share This Page