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Discuss INTERMITTENT WATER PRESSURE LOSS in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. John Taylor

    John Taylor New Member

    Re: Domestic c/h with Vaillant ecoTEC plus 837 boiler.

    For the past 12 months or so, boiler water pressure has intermittently dropped from the normal operating pressure of 1.8bar to 0.3bar overnight, indicated by fault code F75.

    I would re-pressurise the system and monitor pressure for a couple of weeks noting stable pressure then forget about it. A couple of months later, I would wake up to no-heat and/ or no-DHW and re-pressurise again. About the 3rd occassion I called out my local installer/service engineer and advised him that there had not been any slow reduction in water pressure. He did a visual search but could not find water leak.

    The Vaillant service engineer was then called out and replaced faulty water pressure sensor which was 'gunged up'.

    2 weeks later, same problem, woke up to no heat, water pressure at 0.3bar, code F22 this time. My local installer called out, visual search for water leak, none found. I then agreed to him adding C-Tec Miracle Seal to the system. The product information states that it is "100% guaranteed not to clog the system in accordance with application instructions."

    However I have a radiator with TRV set for frost protection, which, by coincidence, won't now heat up when TVR operated to call for heat. I have checked for air-lock and bled the rad, no air or aerated water released, just lots of clear water....no sign of the coloured sealant nor sealing of the 'leaking' bleed valve!.

    Before calling out my service engineer again, I am hoping this forum's experts could help with my queries viz:-

    Q1 - Does anyone know of a case where adding the leak sealant can cause problems?.

    Q2 - Why hasn't the sealant 'sealed' the bleed valve?.

    Q3 - What is the likely reason for the rad not heating up ?.

    Q4 - What other causes of loss of water pressure in Vaillant boilers are regularly recorded?.

    Looking forward to your responses....many thanks.
  2. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Leak sealant is always last resort for me. I’ve heard of and seen no end of problems with blocked AAVs and weak pumps as a result. There were other things that the Vaillant engineer should have checked before leaving which could’ve contributed to your pressure loss. Sadly they are within the boiler and so you’ll need a gas safe engineer to look. Could be a blockage or a part that needs some attention. If you disconnect the radiator does water come out of the offending TRV. If not I’d say the leak sealant has fubar’d it
    • Informative Informative x 1
    Last edited: Jan 21, 2019
  3. John Taylor

    John Taylor New Member

    Thank you Riley for your prompt reply.

    Both the Vaillant service engineer and my Vaillant approved installer checked the boiler internals for water leaks prior to their remedies.

    Referring back to my O.P., I have just thought of a another question.

    Q5 - What would cause water pressure to drop from 1.8bar to 0.3 bar instantly overnight resulting in the 'low water pressure' code F22 to register?.

    Please note that, at no time, during the occasions of my monitoring the water pressure, did I log a slow, progressive drop.
  4. Rob Foster

    Rob Foster Top Contributor!!

    Leak sealer is really not right, some water pathways in the boiler are tighter than your leak and the gunge just gives the boiler a premature heart attack
    Rob Foster aka centralheatking
    • Informative Informative x 1
  5. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    If they are genuinely proper installers then they will tell you that there is not nevessarily A visual internal leak. And I am very surprised that they’ve not tested the relevant parts in order to check this
    • Like Like x 1
    • Useful Useful x 1
  6. scott_d

    scott_d Plumber GSR Top Contributor!!

    Check all rads for leaks when hot and cold.
    Put a balloon or clear bag over the external pressure relief pipe.
    • Like Like x 4
    • Useful Useful x 1
  7. Rob Foster

    Rob Foster Top Contributor!!

    Top Up Mate from Flowflex cures the problems with invisible leaks on pressurised systems Rob Foster aka centralheatking
  8. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Rob there is every chance that it’s a part in the boiler that has not been properly tested and is causing the boiler to cough out. This product will just mask the problem
    • Agree Agree x 1
  9. John Taylor

    John Taylor New Member

    Is that in addition to Miracle Seal already used?.
  10. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Miracle seal should’ve been the absolute last place they went in terms of a repair. It sounds like a very lazy engineer to me
    • Like Like x 1
    • Agree Agree x 1
    Last edited: Jan 21, 2019
  11. John Taylor

    John Taylor New Member

    Hi Riley, What does 'cough out' mean?. my guess would be excess water pressure relief-valve opens!. For my Vaillent would this be greater than 3bar and if so, how/why would the pressure rise to that level?.

    PS - Doh!, I can't work out how to insert quotes. Other forums I use have a different routine. Please can someone instruct me through the correct key strokes.
  12. rpm

    rpm Trusted Plumber Top Contributor!!

    Bottom R/H corner of post you want to quote.
    • Like Like x 1
  13. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Yes cough out is the PrV opening and there are likely reasons why
    • Like Like x 1
  14. Matchless.plumb

    Matchless.plumb Trusted Plumber GSR

    Can definitely agree with Riley here. Perhaps they never checked the parts properly and therefore leading to a quick pressure loss. It’s always difficult to locate a leak like this as it can be anywhere and everywhere. But as many engineers have suggested above all the obvious things should be checked first.
    • Like Like x 1
  15. John Taylor

    John Taylor New Member

    1. Re: Water pressure loss - no further incidents since Miracle Seal added to circuit.

    2. Re: Conservatory radiator not heating up - My C/H service engineer on holiday abroad returned my telephone call and advised me to remove TRV thermostat unit and check movement of valve spinal having given it a spray of WD40.

    Followed advice, spindle ok but still no heat.

    Back to basics ("turn it off, turn it on", as the PC tech guy would say ), so I checked the lock shield valve, noted it was only partially open, as set 10 years previously, and opened it little more. Yappa dabba do, instant heat:). Monitored TRV activity, room temp control back to normal.

    I assume that the lock shield was open at the minimal position for normal water flow and therefore the Miracle Seal actually blocked off the flow:eek:. I can't think of any other explanation.

    It's now fingers crossed, hopefully no more low water pressure alerts.

    Meanwhile thanks to everyone for their advice.:D:D:D
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