Toilet cistern does not stop flushing

Every few months our 24 year old slimline concealed cistern does not properly stop flushing. It continues flowing at a fast dribble. How can it do this when the volume of water flowing surely is insufficient to maintain a siphon? I suppose it means that the suction of the column of water exiting the siphon is greater than the head of the water entering the siphon, and that no air has entered the columns (why not?) to break the siphon.


I can stop it by unscrewing the joint by my finger to let some air in.


Failing someone offering a solution here, am wondering about drilling a small (say 1-2mm) hole by my finger in the picture. This maybe would be small enough to not impede the main flush, but large enough to let in enough air to break the siphon


We have 2 other identical cisterns and they do not give the same problem. Have replaced the plastic diaphragm on some.

Couple of reasons
First is the button or cable jams a bit and water continues to syphon at the same rate the water enters. Toilet continuously flows.
You normally have to fiddle with button or cable to reset syphon. Happens with ours around once a year.

Other reason. Syphons are shorter in height now. If cistern fills up because inlet fault the water overflows through syphon into the toilet. Cisterns don't need an overflow pipe now..

Wayners said:

You normally have to fiddle with button or cable to reset syphon.

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Thanks. I try that and it does not stop the dribbling. Only breaking the siphon joint to let air in does it.

Does the handle/syphon return down?

Syphons just stop flushing. If it works maybe change how handle is connected. New handle can be bought from Screwfix cheap if in poor condition

CBW said:

Does the handle/syphon return down?

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Yes it's fine. No mechanical issues with the handle. Once started it will carry on dribbling no matter how much pumping I do on the handle.


PS Why is the font size for this forum huge? No other website comes out huge.

@echase
I guess your on pc and have zoom switched on. That will work only on this site. Lower it back to normal.
That's my guess as the font here is not big