I've got a problem that I think has only started occurring in the last week or so, my toilet seems to keep draining for up to hours after it was last flushed, and weirdly so it seems to be affecting the en-suite upstairs as well.

I'll start by adding I know little to nothing about plumbing/toilets

The downstairs one (that was flushed most recent) has the water level just about inline with (i think) the overflow valve, and it's just currently constantly draining at a slow steady rate. Image

At the meantime the upstairs one is seemingly very low level in the tank, but just isn't filling up, even if I manually try adding more, this one is also draining, just very very slowly. Image

Is there a simple fix? Do I just need to put more water in the whole system, or is there something I'd possibly need to get a plumber in for?


I've watched a few youtube videos, mostly about replacing the cistern for a new one (which I've just bought, doesn't solve the problem) although I think the issue specifically seems to be that the water is just going in the overflow, there doesn't seem to be a problem with the valve at the bottom, when I flush it, it does stop for a little bit until the water hits the overflow valve and then just keeps going, it's as though it's never told to stop filling the tank back up

2 Answers 2


Right ok, whilst I'm still not an expert by any means... but... I think that it's fairly easy to diagnose problem.

First I checked out a few youtube videos on the problem, most people suggested the issue was the flush valve/cistern (couple of videos on fixing that here, link 1, link 2.

I actually bought and replaced the flush valve on my toilets except that wasn't the problem.

Part of what really helped me was trying to take my time to realise why it was still running after the flush. I turned my water pressure lower so it would fill up at a slower rate, then I flushed the toilet again and watched each part until I saw what wasn't working as it was meant to.

The first link above helps to describe the process, but in very simplistic terms for people in a similar situation, when you press the switch it presses a release on the valve to eject all the water in the tank, once it reaches it's 'empty' state (which you can change on your valve) the mechanism will close back up and create a container for the water to fill back up again, this is step one in trying to figure out the issue, it's why a lot of the problems are related to the seal on the valve.

That wasn't my issue, then, as the water is filling, the level rises until it reaches the float gauge (where the water is coming out) and the float is then intended to lift the lever on the gauge to close it when it reaches it's fill capacity (again, you can change this)

This was my problem, the float was being lifted, except the valve inside the float gauge was clogged or damaged and wasn't stopping the water entering the tank when it reached it's highest point, and then the water was just flowing through the overflow pipe and down the toilet.

So the simple fix was just to change the float gauge, they're all of about £10 at toolstation, and I fitted it with no problem

Hope this helps someone in the future


You have 2 problems.

1 - your Flush Valve, the bigger white piece in the middle, likely needs its rubber washer replaced at the bottom. The tank/cistern draining or emptying on its own into the toilet's bowl is always an indicator of that. Cheap, but on that valve style it could be difficult for a rookie to figure out.

Rubber Washer and Flappers (on toilets that use them) can require replacement as often as every 5-years. Normally though, it's every 10-years or slightly more.

2 - your Fill Valve, the blue topped piece on the right, needs adjustment in possibly both toilets. The CL line (Cistern Water Level, for the manufacturer's proper and intended operation) on the back of the tank is typically where you want the tank to fill to and hold at, slightly under is ideal, until an intended flush.

2 can be a bit tricky if the toilet components were replaced, which yours seem likely to have been done...based on the rust amount on the wall screws.

Regardless, the goal in your case is to get and keep the water level 1-inch/25mm below the top of the Flush Valve's overflow. This, is done by either adjusting the Fill Valve's float individually or by adjusting the Fill Valve's tower height entirely...if you have that type.

3 - you should tightly shim and then screw the other side of the tank on the toilet in picture #2. Porcelain doesn't like flex or movement and the hole is there to ensure the tank doesn't split wide open in an instant.

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