Vaillant Combi Boiler Losing Pressure

Discussion in 'Plumbers' Talk' started by Nim7, Feb 23, 2018.

  1. Nim7

    Nim7 New Member

    I am currently experiencing a really frustrating problem with my Vaillant Ecotec Plus 831 Combi boiler (installed 9 years ago)

    Below is a summary of where I am currently at with it:
    1) Main heat exchanger has been replaced by a Vaillant engineer as he initially thought it was leaking however since this has been changed, the pressure keeps dropping
    2) The pressure relief pipe is NOT leaking and hence the pressure relief valve has not been activated
    3) There are no signs of any obvious leaking on any of the radiator valves on my radiators
    4) There is no air in the radiators for me to bleed either
    5) I repressurise the boiler to 1.5 bar and the boiler pressure is lost overnight even though the flow and return pipe has been isolated under the boiler (I did this as a test to confirm whether it was the boiler or the system)
    6) The severe loss of pressure only started after the main heat exchanger was replaced by a Vaillant engineer
    7) The boiler shuts down overnight with an F22 fault code and therefore i have to repressurise it again to get the boiler going
    8) A second Vaillant engineer attended this afternoon and opened the boiler cover and could not find any leaks inside of the boiler and ran the P0 and P2 test programs. Shortly after he left, pressure is still being lost
    9) The pressure level never reaches the critical level on the boiler when the heating is switched on

    So therefore I am really stuck and don't know where to go with this one! Does anybody have any possible ideas on what could be causing the pressure inside of the boiler to be lost so rapidly? I phoned Vaillant technical for help who simply said that another engineer would need too attend to try and find the source of the leak inside of the boiler if the boiler has been isolated from the return and flow valves. Please would somebody be able to shed some light on this misery?
     
  2. retiredsparks

    retiredsparks Super Member

    See my post previously. similar problem but not on boiler.
    Maybe bypassing divertor valve ?
    Did they check the pressure vessel ?
    Let us know when solved
    Rs
     
  3. Dave does Gas

    Dave does Gas Screwfix Select

    Simple test you can do to prove if its the boiler or the system. Top the pressure up to about 2 bar, Isolate the flow and return (Left and Right pipes) underneath the boiler You'll need a 4mm allen key. Turn the demand for heating off.
    Go out for a while, long walk and a pint or two. In a few hours check the pressure if its dropped boiler issue. Open up the flow and return, if it drops system issue.
     
  4. Nim7

    Nim7 New Member

    Thank you for your reply. This is the method that I have tried and I explained this to the Vaillant engineer (Engineer 231 at Vaillant) that attended this afternoon. I isolated the flow and return valves using a 4mm allen key and turned both control knobs for the hot water temperature and CH temperature to the minimum and the boiler is still losing its pressure. During his visit this afternoon, he simply tried to find possible leak areas inside the boiler but seemed a bit confused himself on why it was losing pressure with both flow and return valves isolated underneath the boiler.

    There is no evidence of any leaks on the divertor valve (as according to another engineer I have the old divertor valve as the newer ones from Vaillant are apparently known for leaking). Although I did not see the Vaillant engineer check the pressure inside of the expansion vessel as didn't think of this until retiredsparks mentioned this on his reply.
     
  5. terrymac

    terrymac Screwfix Select

    As I understand it ,op has already done what Dave does gas suggested ie isolated flow and return at boiler ,and boiler lost pressure overnight. So this leaves internal boiler leak , loss thru prv or condensate pipework ( including the Internal parts that facilitate this) or the flow / return isolator/s are not fully closing and there is a system leak. Its Impossible to diagnose via the forum ,only an engineer on site with the skills and the will to apply them can do that.
     
    Johnst1a likes this.
  6. terrymac

    terrymac Screwfix Select

    The expansion vessel if at fault would cause prv to open ,or there would be water visible internally as would be
    with diverter. All of which would be unlikely to be missed by two engineers unless they were completely incompetent , which is very unlikely. By the way were you losing pressure originally ,and that's why the HEX was replaced ?
     
  7. retiredsparks

    retiredsparks Super Member


    Terry, can the DV can leak internally to HW side on this model ?
    No external signs ?
    RS
     
  8. Nim7

    Nim7 New Member

    Yes Terrymac, your completely correct as I do not currently have any problems with the PRV valve discharging any water and the PRV Pipe is completely dry outside when I have checked it. The pressure gauge does not reach the critical level when the heating is switched on either. I did stand quite close to engineer whilst he was inspecting the internal parts of the boiler and did not see any evidence of the diverter valve leaking and there was no water on the bottom casing of boiler.
     
    Last edited: Feb 23, 2018
  9. terrymac

    terrymac Screwfix Select

    If the primary hydraulic system breached to the mains cold you would get pressure increase not pressure drop , think about it ,it would be the same as leaving the filling loop open RS.
     
  10. terrymac

    terrymac Screwfix Select

    Nim ,please answer my question regarding Original reason for HEX replacement ,thanks
     
  11. Nim7

    Nim7 New Member

    Yes the heat exchanger was replaced yesterday as the Combi boiler used to lose 0.2 bar of pressure each day and I was constantly refilling the boiler each day as well. The fault with the Main heat exchanger was originally diagnosed by Vaillant last month and hence they ordered a new HX for me which got fitted yesterday. They could not find any evidence of a leak inside the boiler in the visit either and hence they rounded it down to a fault with the HX. The part seemed scaled although there was no corrosion when it was removed but according to the Vaillant engineer, it is not always possible to see tiny cracks inside. Hope this all makes sense to everybody.
     
  12. Mike83

    Mike83 Screwfix Select

    I wonder if either the flow or return isolation valves are passing making the test invalid.
     
  13. terrymac

    terrymac Screwfix Select

    Thanks Nim. So the higher level of pressure loss has only raised its head since yesterday ,would point towards the fitting of the new HEX. So what was the diagnosis of the engineer today ?
     
  14. terrymac

    terrymac Screwfix Select

    .mentioned that as a possibility earlier mike ,but now op has clarified some history ....original pressure loss 0.2 bar .diagnosed Hex . replaced hex yesterday now pressure drops greater .
     
  15. Mike83

    Mike83 Screwfix Select

    Should really have read everything rather than just scan over it.
     
  16. Nim7

    Nim7 New Member

    The diagnosis of the engineer this afternoon is that there is no evidence of a leak inside of the boiler and that there maybe a possible system leak. This is his exact report which he has sent back to Vaillant customer services. I am not entirely sure if the flow and return valves are at fault but all I can say is that none of the radiators warm up when both the return and flow isolator valves have been isolated so I take it the valves would be serving their purpose?

    I have also just spoken to Vaillant customer services this evening before they closed their phone line. They advised they will not send out another engineer as I cannot disagree with the notes that have been made by their visiting engineer this afternoon. They recommended getting an independent gas safe registered engineer to prove their findings wrong. Rather disappointing seeing as i am paying Vaillant £50 a month for a repair contract to look after my boiler and controls.
     
  17. Mike83

    Mike83 Screwfix Select

    I wonder if the water pressure sensor was maybe changed. If this was faulty it may explain why the pressure loss now seems greater than previously.

    If possible why not test the heating circuit when isolated (capped)from the boiler.
     
  18. Nim7

    Nim7 New Member

    The pressure sensor was relocated and fitted in a totally different place yesterday by the engineer. It has now been fitted in the top left hand side of the boiler connection tube whereas before it used to be located on the bottom left hand side of the boiler. I have no idea why he did this at all.
     
  19. Mike83

    Mike83 Screwfix Select

    It's normal with the new internal pipes.
    It could give slightly different readings in the new location.
    The old sensor could have been partially blocked giving false readings.
     
  20. Mike83

    Mike83 Screwfix Select

    The leak is either on the boiler or the heating circuit.
    In this scenario I wouldn't 100% rely on the isolation valves doing their Job.
     

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