1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Another "my boiler is losing pressure" post

Discussion in 'Plumbing and Central Heating' started by DavidH1983, 26 Oct 2017.

  1. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    Evening,

    Since having a new boiler, a Vaillant Eco 825 installed at the end of Feb I have occasionally had to top up the water due to low pressure (F22 error). I was doing this around once a month. Last week I did it twice and now this week I've had to do it every morning before being able to access hot water. Not good.

    I have spoken with the company who fitted it who are coming round on Tuesday (I had to barter down from next Friday) to take a look at it but I have a feeling I know what they'll say. That being there's a problem somewhere in the system and the boiler isn't at fault. That may be the case but before they arrive I'd like to try and arm myself with as much info as possible and perhaps try and do some fault-finding myself.

    I'd like to establish if possible where the pressure is being lost. This morning we had hot water. When getting in from work around 8 hours later there was none. The heating hadn't been switched on. I'm not sure if this counts as the heating being isolated from the boiler, I suspect not. If not then how can I do this and make this check? (I will no doubt have to go up into the loft tonight to refill it).

    I can if necessary climb out and get access to the PRV pipe if that helps.

    Finally, will the boiler need to be topped up with inhibitor due to the constant top-ups?

    Many thanks for any help anyone can provide.
     
  2. Sponsored Links
  3. cross thread

    cross thread

    Joined:
    8 Sep 2005
    Messages:
    1,686
    Thanks Received:
    301
    Location:
    worlds end
    Country:
    United Kingdom
    check all rads and valves first
     
    • Thanks Thanks x 1
  4. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    Thanks for the reply. Sorry I forgot to add, all rads have been checked and whilst we did have a tiny bit of leakage on one valve (green oxidation on a copper pipe) this seemed to cure itself. There is no sign of any other leakages as far as I can see. Everything has been bone dry for a while now. I realise this doesn't eliminate pipes and parts of the system I can't see but it's a start.
     
  5. cross thread

    cross thread

    Joined:
    8 Sep 2005
    Messages:
    1,686
    Thanks Received:
    301
    Location:
    worlds end
    Country:
    United Kingdom
    any pipework in a solid floor
     
  6. Iamchamps

    Iamchamps

    Joined:
    24 Sep 2016
    Messages:
    1,043
    Thanks Received:
    164
    Country:
    United Kingdom
    Have you ruled out the pressure relief valve? There should be a valve outside that allows water out if the pressure was to get to high. Tape a small bag round it and see if it fills up with water.
     
  7. Madrab

    Madrab

    Joined:
    4 Oct 2012
    Messages:
    8,554
    Thanks Received:
    2,479
    Location:
    East Renfrewshire
    Country:
    United Kingdom
    Not normally what I'd recommend but if the boiler's new you may get away with using the flow and return valves to isolate the boiler without them leaking. If the pressure still drops, it's internal to the boiler, if not and you then open the valves up and the pressure drops then it's out in the system somewhere.
     
    • Thanks Thanks x 1
    • Like Like x 1
  8. MANDATE

    MANDATE

    Joined:
    6 Mar 2003
    Messages:
    2,328
    Thanks Received:
    134
    Location:
    Manchester
    Country:
    United Kingdom
    Hi David.
    You need to understand how the expansion vessel works.
    When first installed, it is charged with air to approx 1bar.
    This means there is no water in the vessel and note there will be a rubber diaphragm separating the water from the air.
    Now when the water gets heated, it expands and pushes against the diaphragm.
    This compresses the air in the vessel, which results in a rise in pressure.
    This rise, by design is not to go beyond 3bar.If it does then the PRV is designed to open and discharge a small amount of water.
    This results in a drop in pressure, which means topping up is needed.
    So the rise to 3bar has got to be addressed, otherwise the problem will repeat itself.
    Also! Note the PRV once opened may not close properly due to sediment on the sealing face and leave you with small leak.
    Now if the expansion vessel was not charged with air correctly or it has lost some of its charge, its allows water to take space reduces the air space. This reduced volume of air when compressed cause the pressure to exceed 3bar.
    On the expansion vessel there will be a valve similar to a car tyre and this can be the source of a air leak.
    Also a blockage in a flexible pipe connecting the expansion vessel can stop the compression of air and force water out of the PRV.
    Hope it helps
     
    • Like Like x 1
  9. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    Some though this may be accessible from underneath. We have two rooms where I've recently installed solid wood flooring. There are no visible signs of leaking on our ceilings. There is however one rad downstairs encased in a wooden radiator box type thing. The guy who lived here before me loved making useless crap out of wood. I will check this out tomorrow night. The rest of the pipework should be accessible with a little bit of perseverance.
     
  10. Sponsored Links
  11. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    I haven't and this is something I wanted to do tonight. Just my luck it was absolutely chucking it down earlier so I didn't fancy going out onto the sloped roof to check the pipe out. I will do this when it's dry with a bag as you say. Does it matter that air/condensation won't be able to escape if I tape it up?
     
  12. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    By flow and return do you mean the CH flow and return? If you do then this is something I'd like to try and do. It's just a matter of identifying those pipes. I read quite a few posts on here where people had isolated the CH for around 12-24 hours and then monitored the pressure again.
     
  13. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    Thank you for this explanation. I have never seen the pressure (on the digital readout) go above 2.0 bar. It touched 2 bar for a split second and then went to 1.8 as I closed the filling loop. I've read that actually anywhere between 1.2 and 1.5 is absolutely fine. I'm saying this because I don't think the PRV has had a cause to open but I could be wrong.

    Am I right in thinking that in order to recharge the expansion vessel with air I need to get the water pressure to 0 bar first? Do I need to do anything else before filling the expansion vessel with air?
     
  14. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    I am beginning to wonder why all of a sudden the pressure takes very little time to drop. Before it would drop to 0.7 or 0.8, the boiler would cut out but the pressure would hold. Now it just drops to 0.

    Thanks for all the replies. They're helping me to get an idea about where the issue may be. That in turn will help me when it comes to speaking with the plumber.
     
  15. MANDATE

    MANDATE

    Joined:
    6 Mar 2003
    Messages:
    2,328
    Thanks Received:
    134
    Location:
    Manchester
    Country:
    United Kingdom
    Hi David
    Those pressures would indicate the expansion vessel is working as it should.
    When charging a vessel the water pressure must be zero, but the water must be open to atmosphere.
    If the vessel had water in the air space, then it would need to be discharged out of the system as the air pressure applies force to the diaphragm.
    It does sound that your problem is more related to a water leak
     
    • Thanks Thanks x 1
  16. DavidH1983

    DavidH1983

    Joined:
    29 Jul 2016
    Messages:
    93
    Thanks Received:
    0
    Location:
    Lee, London
    Country:
    United Kingdom
    Thanks. Pressure was at 0 again this morning. I topped it up to 1.5 and then got alarmed when I heard gushing water....it was the Mrs flushing the toilet.

    Tonight I'm going to isolate the CH flow and return before repressurising the water. If I'm still losing pressure then ill move onto the expansion vessel. I guess it's a case of process of elimination. I'd like to get these things done before the plumber comes so that perhaps he can explore other avenues.

    I managed to check two out of our six rads. They felt fine. I found it easier to detect water using my fingers and hands rather than a piece of tissue. Are there any other ways I can check?

    Tonight I will check the rad encased in wood. I bet there are spiders in there.

    Thanks again.
     
  17. Madrab

    Madrab

    Joined:
    4 Oct 2012
    Messages:
    8,554
    Thanks Received:
    2,479
    Location:
    East Renfrewshire
    Country:
    United Kingdom
    That's the one @DavidH1983, that will at least identify where the issue is which is what you are trying to achieve? Yes it would be a good idea to top up the inhibitor. Isolate 1 rad, drain it and fill it with 1L of good inhibitor, cant go wrong.

    I would be very surprised if the expansion vessel/prv was the issue here on a newish system, unless it was an out and out failure, if the pressure doesn't increase to 3+bar when the heating is on, then that's not the issue.

    Blue roll - best thing to use to check for leaks as it changes to dark blue with any water on it.
     
    • Thanks Thanks x 1
Loading...

Share This Page