The lever type matters too. Close-coupled cisterns almost always use a side lever or a push button through the lid, while older low-level suites more often run a side lever connected by an external link arm. Ordering a replacement lever without checking which type is fitted is a common cause of parts being sent back.

The second check is a knocking or banging sound, sometimes called water hammer, that happens specifically at the moment the fill valve shuts off rather than during the fill itself. This is far more often a mains pressure issue than a valve fault, caused by the sudden stop of a fast-moving column of water hitting the closed valve and sending a shock through the pipework. A fill valve replacement on its own will sometimes quieten this slightly, particularly if swapping to a bottom-entry valve which fills more gently, but it will not fully resolve a genuine water hammer problem, which usually needs an air-filled arrestor fitted at the supply if it persists.

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A cistern that whistles, knocks or hammers while filling is one of the more annoying faults a customer will report, and it is also one of the quicker ones to run down with a short checklist before a plumber even gets to the van. Two causes account for the large majority of noisy-cistern callouts: a worn fill valve and excessive mains pressure, and telling them apart early saves time on Related Site.