Advent-ures in the MSE Forum... Our Advent calendar is live, helping you discover a new corner of the community each day. Visit the homepage and scroll down

Mysterious pressure loss

I have a Vaillant condensing combi boiler that is losing pressure.

I had a plumber look at it and advised me that the system was losing pressure on the central heating system.

As most pipes are in concrete floors and there are no visible signs of damp I had a trace and access company round to look for it. They can find no leak on the system but whilst they were looking at the boiler they noticed it ejected a large amount of water and they tell me that all it should do is drip to eject the condensation not eject large amounts.

Is this right and does this therefore suggest a problem on the boiler itself?

Many thanks


  • GrenageGrenage Forumite
    2.8K Posts
    Eighth Anniversary 1,000 Posts Name Dropper
    It does rather suggest an issue with the boiler; boilers should not eject water.
  • Alex1983Alex1983 Forumite
    958 Posts
    It’s possible it’s the pressure relief passing, you can prove this by taping a sandwich bag over the termination outside and see if you get any water in it.

    It could be the heat exchanger leaking internally which would then disappear out the condense pipe work, or the more likely that the pipe work is leaking in the concrete floor.

    If you refill the system to 1.5bar and shut the central heating flow and returns and leave it off for 48hrs, if you still loose pressure it has to be the heat exchanger or pressure relief, if you don’t lose pressure open the valves back up and id expect you’d lose the pressure then you’ve proved it’s in the concrete floor.
  • Many thanks for the reply.

    The water is down the condensation pipe not from the prv.

    No leak found on the pipe work in the floor despite an extensive search
  • I seem to share your experience.
    May I ask did you locate the problem ?
  • cajefcajef Forumite
    6.2K Posts
    Part of the Furniture 1,000 Posts Name Dropper Photogenic
    I seem to share your experience.
    May I ask did you locate the problem ?
    Seeing as this thread is two years old and the OP has not been back on these forums for fifteen months I doubt you will get an answer, probably better to keep to one of your original multiple posts about this problem.
This discussion has been closed.
Latest MSE News and Guides

Is your local HSBC closing?

114 branches to shut in 2023

MSE News

Advent Competitions

The countdown is on

MSE Forum

Baileys £10 for 1L at Tesco

When you scan your Clubcard

MSE Deals