Toilet Cistern Noisy When Filling
- How urgent
- Low risk
- Who fixes it
- A plumber
What's happening?
While a cistern refills, water goes through the inlet valve at the supply pressure. A hiss or whistle means it is being forced past a worn washer or a scaled seat. A hum or buzz means the valve's diaphragm is vibrating, often because pressure is high. A bang when the float shuts the valve is water hammer: the flow stops suddenly and the pipe shudders. The noise starts at the inlet valve but can travel through the pipework, so a toilet noise is sometimes heard in a wall far from the cistern. This page covers noise on a normal refill. A cistern that hisses constantly and never stops is on the toilet keeps running page.
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What usually causes it?
- A worn washer or diaphragm in the inlet valve letting water force past it
- Scale or grit on the valve seat narrowing the opening
- Mains pressure higher than the valve is built for
- A side-entry valve in a top-entry cistern, or the wrong valve for a low-pressure supply
- A float arm that closes the valve abruptly, causing a bang
- Unclipped pipework that rattles against a wall when the valve shuts
- An isolating valve left part-closed, which makes the water scream through it
Is it dangerous?
No. The risk is a valve that gets worse until it leaks into the overflow, and a noise that carries through the house at night. A bang that shakes the pipe every flush wears fittings over time.
Can I fix it myself?
Open the isolating valve fully, then partly close it if the noise stops at a lower flow, which tells you the pressure is the problem. Take the lid off, shut the supply, and unscrew the top of the inlet valve to rinse the seat and washer. If the washer is cracked or hard, replace it with the maker's part. Clip any pipe that rattles. If the noise is in the whole house on every tap, the pipes humming or vibrating page covers pressure and valve causes. Do not tighten the float arm so that the cistern under-fills.
When should you call a plumber?
Call a plumber when a new washer or a cleaned valve does not quiet it, when the noise appears on other taps, when the supply pressure may be too high, or when a noisy valve sits behind a concealed cistern.
What will the plumber actually do?
- Identify the inlet valve type and whether it matches the supply, high pressure or low pressure
- Clean the seat and replace the washer or diaphragm, or fit a quieter valve
- Check the isolating valve and the flexible connector for restriction
- Measure supply pressure with a gauge where the noise is house-wide
- Clip loose pipework and fit a pressure-reducing valve or arrestor where the pressure or hammer is the cause
Who fixes this
- Toilet repair and replacement
Questions people ask
Why does my toilet cistern hiss when it fills?
Why does the cistern whistle or hum while filling?
Why do I hear a bang when the cistern stops filling?
Does the noise mean something is leaking?
Sources & References
Before you book, read what to check before a plumber starts.
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