Toilet cistern leaking

3 Oct 2017
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United Kingdom
My toilet cistern it leaking into the pan. It has a Dudley Hydroflo inlet valve which I assumed was leaking but it does close properly. If I shut off the water supply to the cistern it will empty itself into the pan in a few hours. Before I pull the cupboard to bits and remove it all from the wall, does anyone have any pointers as to where to start looking in the cistern? Hopefully it just needs a clean around the seals, but is it likely to be anything else? I can't see any markings on the cistern to identify it... Thanks.
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Sounds like you have a push button style, which the seal underneath will be perished, dirty or have trapped debris - clean or replace as necessary
Try viewing this, also check to make sure the button isn’t stuck in.

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Assuming you have something similar to your picture, and access is reasonable:
1. Isolate the water into the cistern (The picture one has an isolation valve at the end of the flexible hose).
2. Remove the flush valve. This is the green bit in your picture. Try pushing it down slightly and rotating clockwise (looking down) about an eighth of a turn. They are normally held on a bayonet type fixing. Don't force it, but give it a bit of extra twist if it doesn't shift, and / or try anti-clockwise.
3. Check the large rubber washer on the base of the valve, clean / replace it.
4. Clean the seating for the valve rubber which will still be inside the cistern.
5. Reassemble, turn the water back on and check.
Thank you both very much, that's exactly what I needed. They call it the Niagara seal, so now I know what I'm looking for if I need a replacement. And it looks like I'll be able to get the green bit out (thanks oldbuffer for the instructions) without dismantling the cupboard anymore, taking the cistern off the wall, or dismantling any pushfit plumbing fittings which is what I was most nervous about. Result!
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