A button that does not come back up is a valve that never closes
The button is not connected to the water. It pushes a rod, the rod pushes the flush valve open, and the valve dropping back down onto its seal is what stops the flush. So a button that stays down is a rod that is still holding the valve up — which means the cistern is emptying into the pan continuously and the fill valve is replacing it just as fast. There is no “just stiff”. There is a toilet that has been running, quietly, since the day the button first stuck.
Put a number on it. A gap of about three millimetres — the sort you cannot hear over a bathroom fan — passes roughly 0.3 litres a minute. That is 430 litres a day, about 13 cubic metres a month, and at typical municipal rates something like forty to fifty a month on the bill, year after year. The repair, in the three most common cases, costs nothing and takes less time than reading this page.
Then there is the rod, which fails in both directions and the symptoms are opposite. Too long, and the lid holds it against the flush valve permanently: the button has no travel left to spring back, and the valve never seats. Too short, and pressing does nothing much — the valve opens a fraction, the flush is weak, and you press again. The correct setting has a small clearance: press lightly and you hear water start; let go and the button returns with the valve fully closed behind it. Dual-flush cisterns add a wrinkle: one rod does the full flush and the other the half flush, and if they are the same length the half flush stops working properly.
And the cheapest of all is alignment. The button assembly is a single unit sitting in a hole in the lid, and the whole unit can rotate a few degrees — usually after the lid has been taken off and put back carelessly. A few degrees is enough that the rod no longer meets the valve squarely, and the rod then binds against the edge of the valve instead of pressing its centre. The button goes down and stays down. Turning the whole surround half a turn and back often restores it, which is why so many of these get fixed by accident.
Three faults, and the one test that separates them
- The assembly has rotated out of line. The button sinks slightly askew and stays down. Grip the plastic ring around the button and turn it gently, either way, half a turn to a turn, feeling for the point where the binding lets go. No force — old plastic is brittle and the surround cracks long before it gives.
- Scale on the rod, or a lid that is not sitting flat. Hard water leaves a white crust in the gap the rod slides through, and that crust is friction with a very long lever arm. A dry toothbrush and clean water takes it off — not a descaler, because acids attack the plastic. And check the lid: a lid sitting a millimetre proud on one corner clamps the button assembly and holds the button down. That one is fixed by putting the lid back properly, which is a strange thing to charge someone for and a very common cause.
- The rod is a little too long. The giveaway is that it only misbehaves with the lid on. With the lid off the button springs back perfectly; put the lid on and it sits down. On most assemblies the rod telescopes with a clip, or the button's mounting nut sets how far it protrudes — shorten it a little, test, and repeat. Do not shorten it far: too short and you get a weak flush instead. And do not over-tighten the mounting nut either, because that alone can bind the button.
Two things that make it worse
Do not put a bleach block in the cistern. The gel they release coats the rod, the seal and the valve seat, and it is sticky enough to turn a free-moving part into a sluggish one — while also ageing the plastic. If you want the bowl clean, clean the bowl. And never force a plastic rod or a locking tab: they are already a decade old in most cisterns, and a snapped rod turns a free fix into a twenty-dollar assembly. Photograph the inside before you take anything apart — reassembly is much easier with the picture.