Boiler constantly losing pressure.

Discussion in 'Engineers' Talk' started by Dougie1702, Mar 9, 2018.

  1. Dougie1702

    Dougie1702 New Member

    Hi,

    As title says, my boiler it consistently losing all pressure overnight when cold. (Been doing it for months now so, no signs of any water contamination on ceiling etc)
    I have had my local gas engineers out four time now, I've had a leaking pipe inside the boiler replaced, I've had the expansion vessel recharged and all visible pipes checked for leaks.
    The boiler works perfectly all day/night until it goes off at night then won't fire in the morning as the pressure is so low.

    The last engineer that came out, I mentioned a knocking noise to him, which he said is the pump on the way out (never mentioned it until I said to him). Could this be the cause of the drop of pressure overnight?

    I also don't think it's the PRV as I don't seem to have any leaking water outside where the drain valve is... And the pressure only rises slightly when the boiler is running.

    Have you guys any ideas? As I am fed up of constantly having these guys out for them to do nothing to solve it!

    Cheers.
     
  2. Mike83

    Mike83 Active Member

    Need more info.
    Make and model of boiler?
    What tests have been carried out so far?

    Could be leaking pipework out of view. (Under floor)

    Could be leaking heat exchanger on boiler.

    If pressure is dropping overnight it is a fair sized leak. Shouldn't be to difficult to eliminate either the boiler or system from the equation.
     
  3. Dougie1702

    Dougie1702 New Member

    Sorry, it's a Vaillant Ecotec 28. Around 8 years old.
    All checks done by engineers have been visually inside the boiler from what I have seen. New bits of rubber pipe connecting two copper pipes was replaced as it was leaking, didn't fix it.
    Last guy re-pressurised the expansion vessel, checked visible pipes and rads for leaks.

    Still as bad, if not worse now that he has repressurised.

    Cheers.
     
  4. Mike83

    Mike83 Active Member

    If vessel and prv are ok, and also all the rads and visible pipework are fine, then checking the heat exchanger would be my next step.

    Two ways to check the heat exchanger.
    You could top up the pressure to 1.5 bar then close the flow and return isolation valves. Do not use the heating or hot water.
    Observe overnight. If the pressure still drops it sounds like the main heat exchanger.
    If the pressure doesn't drop until the isolation valves are opened then the leak will be on the pipework or rads.

    You could also disconnect the condensate pipe from the bottom right of the boiler and check if water is coming from the pipe. Top pressure to 1.5 bar and observe if water comes from the pipe. You must not use the boiler during this test. Turning the boiler off electrically is best.
     
    terrymac likes this.
  5. Dougie1702

    Dougie1702 New Member

    Could the faulty pump be causing cavitation do you think? And it's losing pressure that way? Or is the pressure drop too severe for that?
     
  6. terrymac

    terrymac Active Member

    No it aint that. Follow Mikes very good advice. Its exactly what I would do to establish if its loss at boiler or on your system . do you have pipes buried in concrete floor ,or in a void below floorboards ?
     
  7. Bob Rathbone

    Bob Rathbone Active Member

    I agree with Mike 83 with one possible exception. The pressure relief valve on the boiler may be leaking by, this is on the boiler side of the isolation valves and will give the same results as heat exchanger leaks.
     
  8. terrymac

    terrymac Active Member

    [From op's original post ..…..

    I also don't think it's the PRV as I don't seem to have any leaking water outside where the drain valve is...

    Seems the op had already ruled that out of the equation
     
  9. Dougie1702

    Dougie1702 New Member

    Local gas engineer out again yesterday, he ruled out heat exchanger, prv and re-pressurised the expansion vessel.
    Pressure dropped again overnight.
    I just find it strange that it loses no pressure whatsoever if I keep the boiler on, as soon as it's off, over 4-5 hours it's emptied again!
    Got a load of air out of the bathroom radiator this morning, this didn't have this air 2 weeks ago... Is that because the pressure?

    No pipes under concrete floor, under floorboards in the downstairs, yes.

    Is the next step then, floorboards up?
     
  10. terrymac

    terrymac Active Member

    If you tonight follow mikes advice ,I.e isolate flow and return pipes at boiler ,leave boiler off all night and see if pressure has dropped the next morning. Note the boiler and rads must have cooled for an hour and then make sure pressure is 1.5 bar ,and then isolate flow and return pipes at the boilers isolators. The engineer May have drawn the wrong conclusions ,but doing the above will clarify whether loss is from boiler or pipework / rads side. If it turns out to be the latter ,then start lifting floorboards
     
  11. Mike83

    Mike83 Active Member

    You need to be absolutely sure it's under the floor before lifting boards.
    A simple overnight test will clear things up.
     
  12. Dougie1702

    Dougie1702 New Member

    This might sound daft, with being pretty crafty handed, I don't know how to isolate the flow..
    Can anyone explain?
     
  13. Mike83

    Mike83 Active Member

    If the engineer was only out for a short while it may not have been a conclusive test.
    When the boiler is running the pressure rises. This could mask any pressure drop until the system cools.
     
  14. Mike83

    Mike83 Active Member

    The 2 22mm pipes at the right and left are the flow and return. It's a 4mm Allen key I'm sure to isolate.
     
  15. Dougie1702

    Dougie1702 New Member

    Thank you. I'll have a look later, and give you a shout if I can't identify it and add a photo!
     
  16. Mike83

    Mike83 Active Member

    Plenty people on this site will help.
    Get all the baths and dishes done before this test. Also turn the heating off a hour before.
    Boiler will be off until the next morning usually.
     
  17. Dougie1702

    Dougie1702 New Member

    The two on the left and right? Not an allen key, it is a cylinder in the centre, but I think a half turn on a flat headed screwdriver will shut it off yes?
     

    Attached Files:

  18. Mike83

    Mike83 Active Member

    Far left and far right.
    An Allen key will fit in the hole in the centre. Works better than a screwdriver.
     
  19. Dougie1702

    Dougie1702 New Member

    It's just a hollow cylinder that's in the centre, no hex shape for Allen key to fit. Just a half turn to the stop shoulder?
     
  20. Mike83

    Mike83 Active Member

    If you have Allen keys try. I'm sure they do fit inside.
     

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