Vaillant boiler losing pressure

Discussion in 'Plumbing and Central Heating' started by Patrick_, 5 Dec 2021.

  1. Patrick_

    Patrick_

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    Hi,

    I renovated my flat earlier this year and installed a new CH system as below:
    * Vaillant ECO Tec Pro 24 combi boiler
    * Nest Thermostat
    * Water UFH for living room
    * Radiators for bedrooms

    Everything above is new, including the pipes.

    Yesterday the boiler stopped working, showing F22 error code and 0.5 bar pressure. I turned heating to OFF via Nest thermostat, waited for 10 min, and turned heating on again. The boiler then worked again, water pressure increased to 1.5 bar, and I had both CH and hot water.

    Today the same thing happened again, and I had to turn heating OFF then ON to get the it work. The Nest thermostat never reports any error (despite room temp never goes up). I had to look at the boiler display screen to get the error message.

    Do you think there is a leak in my central heating system..? Or there can be other causes? Thank you so much!

    thanks
    Patrick
     
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  3. CBW

    CBW

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    Leak in the system, prv issue or expansion issue is likely.
     
  4. terryplumb

    terryplumb

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    Do you have to top up pressure ,or does it not fall below 0.5 bar ,and not rise above 1.5 bar when heating is on ?
     
  5. Patrick_

    Patrick_

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    It didn't fall below 0.5 bar when the boiler refused to work - it was precisely 0.5 bar.
    What I did last weekend was just turn heating off and on again. I didn't top up pressure.
    And when the boiler was running again to heat up CH, the pressure was 1.6 bar.

    I was also suspecting a leak...

    Update:

    The company that renovated my flat supplied and fitted the entire heating system and they gave me 1 year warranty for parts and work.
    Today the company manager came and took a look.
    He didn't deny a leak is the likely cause, but we couldn't found any wet areas near the radiators / UFH manifold / boiler pipes, etc.
    He is not interested in sending someone to check the internal parts of the combi boiler, at least not at this stage. I guess that adds to his cost.
    So he showed me how to top up pressure with the filling loop, and we topped up the pressure to around 1.8 bar when heating is on.

    The manager also told me boiler pressure dropping to 0.5 bar 'a few times per year' is 'common'. And I should just keep an eye on it and top up pressure from time to time. Only when the pressure drops 'very quickly' should I be worried. I'm not very sure about this. What do you think...?

    At the end of the day, if the leak is inside the combi boiler, such as a prv or expansion issue as CBW mentioned, it will actually be a better outcome. My worst nightmare is a leak somewhere in the concealed pipes or joints... The manager told me his plumber pressure tested all pipework before concealing them with the finishes, and a leak in the pipes is 'extremely unlikely'. Is it possible to check whether there is a pipe leak when most of the pipes are concealed...?
     
  6. Harry Bloomfield

    Harry Bloomfield

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    It doesn't quite ring true, in as much as the the way I read it is - the boiler shut down on water pressure failure, then without you topping it up (did you, or not?) just off then on and the pressure came back up to 1.5 - is that correct?
     
  7. Patrick_

    Patrick_

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    That is correct. Without me topping it up, just off then on the pressure came back up to 1.5.
     
  8. Harry Bloomfield

    Harry Bloomfield

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    That is very different. As water in a system heats up, it expands pressure goes up, as it cools it goes down. Yours seems to be doing the opposite, so not a leak. I would guess at either the pressure sensor is faulty, or the PCB. It needs a Gas Registered guy to sort it out.
     
  9. CBW

    CBW

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    Guesswork is expensive, especially for a pcb, which I’d say is 99.99% not needed.

    @Patrick_ it sounds more likely an expansion issue, as all you did was turn off and on again at 0.5 bar and it rose to 1.5 bar. 0.5bar is low pressure, but F22 is the fault that prevents it from working.
     
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  11. Harry Bloomfield

    Harry Bloomfield

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    Yes, guesswork can be expensive, but it is not at the OP's expense nor his problem to resolve.

    How can it possibly be an expansion issue, when the pressure goes up, instantly presumably on the boiler cooling? The only thing which fits the circumstances described, is pressure sensor of PCB related.
     
  12. CBW

    CBW

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    Because, if you read it properly, you’ll find it wasn’t on cooling
    We don’t know who owns the flat, so could be at OP’s expense
    No it isn’t the only thing, and you’ve quoted two things :rolleyes::LOL:
     
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  13. HERTS P&D

    HERTS P&D

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    Chris - harry does like to have a guess at most of the plumbing problems on here.

    Andy
     
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  14. Harry Bloomfield

    Harry Bloomfield

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    Nose put out again?

    I suggest you read it properly, what the OP actually wrote.

    He clearly stated the pressure increased on cooling / on the heating going off and without him needing to top it up. I even asked the OP the clarify that point and he confirmed it. The OP also said he renovated his flat, which suggests he owns and is responsible for it.
     
  15. Harry Bloomfield

    Harry Bloomfield

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    Don't be such a fool Andy - Guessing is a standard diagnostic technique employed in all problem solving. You look at an issue, make a guess at the likely cause of the problem, then examine your guesses with more diagnostics, discounting the guesses which do not fit the circumstances. So you progress, until the only thing left is the actual fault or cause. I don't know of any engineers in any discipline who use any other process, than stating with an initial guessing process.
     
  16. HERTS P&D

    HERTS P&D

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    Sorry, did you say 'make a guess'?

    :ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO:

    Andy
     
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  17. jeff the gasman

    jeff the gasman

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    It’s nothing an annual service won’t fix. Vaillant are renowned for this and I dare say the expansion vessel runs on its limit.
    Small temperature changes can help bring the boiler back on. As well as making it go off again.
     
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