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Vaillant boiler pressure loss - correct diagnosis?

Discussion in 'Plumbing and Central Heating' started by Rich O, 23 May 2021.

  1. Rich O

    Rich O

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    Hi All,
    I have a Vaillant Ecotec Plus 637 with an unvented hot water tank that was installed about 2 1/2 years ago. Not under warranty as missed the first service and then Covid...

    There was always a small leak from the hot water tank PRV but I recently had this replaced and now no leak from that tundish. I had assumed that problem was linked to the need to periodically re-pressurise the boiler but this is still being required (more often recently).

    I first checked the obvious things, went all over the house looking for the smallest of leaks in the radiator circuit and found nothing. Boiler PRV had a bag over it and is bone dry. I've been frequently checking the boiler system pressure and I've never seen it much more than 2 Bar so don't have any reason to suspect the expansion vessel.

    So yesterday after lots of searching on here I connected the distillate pipe to a bucket and with the boiler off after a few hours I got a release of 150ml of water (initially set to 2 bar, noted as 1.9 Bar by the afternoon). There was an amount of ferrous particles in it. I believe the Vaillant heat exchangers are stainless so there shouldn't be any ferrous content in the drain? I can also see an amount of particulate in the distillate sump as it's clear plastic, I confirmed it is magnetic with a magnet. The 'water' also has a smell which reminds me of fernox treated water, should the distillate be odourless?

    Today I did a further test, I noted the start boiler pressure @ 10am of 1.8 Bar. Then turned it off. By 14:30 I had collected another 'dump' of 150ml, left it for longer and at 20:00 there was a second dump of a similar volume. Obviously its has been stone cold through the day so this makes me suspect a leak in the heat exchanger. After that I turned the boiler back on and it's at 1.6 Bar.

    Do people agree with this diagnosis? It is taking about a week to drop low enough for the boiler to cut from pumping up to about 1.5 Bar so this amount of leakage feels about right.

    Looking at the Vaillant web site, it has two repair options. The fixed price doesn't include the heat exchanger or the expansion vessel. this leaves the repair & care plan which does and totals £311.88 (https://www.vaillant.co.uk/homeowners/repairs-servicing/repair-options/#image_text_1). Does that sound like my best option? I think getting an independent plumber would be more expensive if it's the heat exchanger as that part alone is more than this amount.

    Thanks for any comments!

    Cheers,
    Rich
     
  2. terryplumb

    terryplumb

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    Certainly sounds like the heat exchanger . If you can have it replaced for £ 300 ish ,then go for it.
     
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  4. ianmcd

    ianmcd

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    Call Vaillant and ask if you get them to service it would they reinstate the warranty
     
  5. Rich O

    Rich O

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    Thanks both, I'll follow up the options...
     
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