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Cold water in DHW, thermostatic shower valve / Vailant VCW 242 Boiler

Discussion in 'Plumbing and Central Heating' started by cherrymetal, 12 Dec 2018.

  1. cherrymetal


    1 Aug 2009
    Thanks Received:
    United Kingdom
    Ok, probably some dumb questions here, but I need to go through a process of elimination.
    The DHW from my Vailant VCW 242 boiler is not particularly hot. I can get it hotter out of the hot tap if I run another cold tap (which reduces the flow from the hot tap).
    So.… eventually I came to the conclusion that there is cold water flowing through the thermostatic shower valve (Meynell viscount). I've replaced most of the bits in the shower valve and everything seems to be working as it should (although its not all that hot unless I wind the cold water flow right down - on an isolating stop tap that feeds the shower)
    I did notice that the flow metering valve was missing from one leg of the shower valve so I thought that was the solution, so I've just fitted a new one, and no change.
    I've done a flow check from the hot tap in the bath, and I think this boiler should produce 9l/min? I'm getting closer to 11 or 12, and this doesn't really seem to change much with reducing the flow of the DHW at the boiler. Most telling is that there is still water flowing from the hot tap in the bath when the DHW flow valve at the boiler is closed...
    So I'm thinking of fitting a check valve to the hot water feed to the shower - my thinking then that cold water will not pass back along the hot water feed and diluting my hot water??
    Does any of this make sense?
    Other points of note, I've replaced the DHW heat exchanger and the DHW temperature dial doesn't seem to make any difference at any point in its range...
    I don't know what else to do!
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  3. Gasguru


    9 Sep 2005
    Thanks Received:
    United Kingdom
    It sounds like you're on the right track. As you say fit a check valve to the shower hot feed as there seems to be a problem with the shower letting by when it's off.

    You could also read the FAQs on gas rating the boiler...by this age the burner operating pressure could well have drifted...I often find they are a little low reducing performance.

    The temperature gauges are normally broken on VCWs of this age.
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