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Unvented cylinder query

Discussion in 'Plumbing and Central Heating' started by Stevo_78, 10 Jun 2021.

  1. Stevo_78

    Stevo_78

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    Hi

    I wonder if anybody can enlighten me to what my problem may be.

    I have recently drained the CH and filled it back up, bleeding all the radiators.
    The system has an unvented cylinder with two zone valves. When the valves are fully open there is hardly any noise from the cylinder and the rads heat up fine. All rads heat up from bottom to top so pretty sure no air left in system. When these values are in auto and the control is on, same scenerio. But when on auto and the control is off (24/7 currently) there is no heat from the rads, so valves are working, but since I drained the system I can here a constant flow of water from the vicinity of the primary coil.

    The cylinder is upstairs on the landing and I can hear the gushing sound downstairs. If I turn off the boiler or water supply it eventually stops after a few minutes. The pressure is stabile at 1.5bar and the fill loop is shut off at both valves, so it is really puzzling me why am am getting this noise.

    Any suggestions would be greatly appreciated.
     
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  3. oldbuffer

    oldbuffer

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    Could be air in the hot water cylinder primary coil. See if there is a bleed point from the top primary coil entry to "up in the air". If so, with system off and cold, release air. You might have to repeat a couple of times.
     
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  4. Agile

    Agile

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    Without seeing the pipe layout it is difficult to give you generic advice.

    Many installers do not bother to add air vents as we can bleed air at any compression joint. It is not very correct or user friendly but a lot quicker for the installer! So potentially a bit cheaper for the homeowner. It is the installer's job to remove air at installation and they have to deal with any inconvenience.

    If bleeding the system around the cylinder you need to set the motor valves to the mechanical open setting. Most have a lever to do that. It could also be necessary to set to heat the cylinder for a few minutes so the pump can push any air round the system towards the bleeding point. Probably two or three times!

    We could advise further if you could post a photo showing all the pipework around the cylinder.
     
    Last edited: 11 Jun 2021
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  5. BoilerBob

    BoilerBob

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    Don’t forget to work on an unvented cylinder you have to be registered as they come under G3 of building regs. Bob
     
  6. Stevo_78

    Stevo_78

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    So the general consensus is that there is air in the hot water cylinder. I am not sure if there is a bleed valve so it looks like I will have to call in somebody to have a look if I can't touch it. I have attached a photo of the pipework if any help.
     

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  8. BoilerBob

    BoilerBob

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    There’s an air bleed on the vertical pipe the pump is on. Bob
     
  9. Agile

    Agile

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    There is also another potential problem.

    There is a braided pipe going up out of sight and this has a valve on it which is turned off !

    Depending on where it goes to it might need to be turned on if it is to an expansion vessel. But if it is part of a filling loop then it needs to be off.

    Most people would probably take the view that bleeding air using the brass bleed vent is not part of "work" on the system that needs the training and registration.
     
  10. Stevo_78

    Stevo_78

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    The braided pipe is part of the filling loop.
     
  11. Stevo_78

    Stevo_78

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    Is the air bleed the cap at the top of the vertical pipe?
     

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  12. polesapart

    polesapart

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    Yes.

    The unpainted brass thumbturn.

    Latch HW valve open and cautiously loosen, not remove, preferably with cool system water and boiler off.

    Have towel handy.
     
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