Why does my toilet keep running after flushing?

The most common cause is a worn flush valve seal that does not close properly after the flush, allowing water to leak continuously from the cistern into the bowl. The fill valve then keeps topping up the cistern. Other causes include a stuck float arm, a faulty fill valve or a chain that is too tight on older flush mechanisms.

How can I tell if my toilet has a silent leak?

Put 5 to 10 drops of food colouring into the cistern. Do not flush for 15 minutes. If colour appears in the bowl, water is leaking through the flush valve. This catches even slow, silent leaks that you cannot hear but that still waste hundreds of litres a day.

How much water does a running toilet waste?

A continuously running toilet wastes 200 to 400 litres of water per day. On a metered supply in the South West Water region that adds roughly £100 to £300 a year to your bill. Slow, silent leaks waste less — typically 30 to 100 litres per day — but still add £20 to £50 a year if not fixed.

Can I fix a running toilet myself?

Yes, if you are a confident DIYer. Replacing a flush valve washer or a fill valve are straightforward jobs once you have isolated the water supply. A full flush valve replacement is more involved because the cistern has to be removed. If the toilet is old, the ceramic is fragile or you are not sure, a plumber will do the job in 30 to 60 minutes for £80 to £150.

How long does it take a plumber to fix a running toilet?

Most running toilet repairs take a plumber 30 to 60 minutes. They will arrive with the common replacement parts (flush valve, fill valve, washers) and diagnose the exact cause in the first 5 minutes. The repair itself is the bulk of the visit, plus 5 minutes to test for leaks.

Should I replace the whole toilet or just the parts?

Replace the parts if the toilet is under 15 years old, the ceramic is in good condition and the issue is mechanical. Replace the whole toilet if the pan is cracked or chipped, the ceramic is heavily limescaled and unattractive, the cistern is plastic and brittle, or you are renovating the bathroom anyway. A new close-coupled toilet supplied and fitted costs £250 to £500.

What is the most common cause of a slow-filling cistern?

A partially closed isolation valve under the cistern is the most common cause and the easiest to fix — open it fully with a flathead screwdriver. If the valve is fully open, the next likely cause is a blocked inlet filter on the fill valve, which is especially common in hard-water areas like Exmouth. The filter unscrews for cleaning.

Running Toilet? Here's How to Diagnose and Fix It

A continuously running toilet is the most common toilet fault — and the most wasteful. Here is how to work out what is wrong, what to try yourself and when it is time to call a plumber.

Find a Plumber

Why a Running Toilet Matters

It is not just an annoying sound — the cost adds up faster than most homeowners realise.

Up to 400 litres per day

A continuously running toilet can waste 200 to 400 litres of water every day — enough to fill four bathtubs. Over a year that adds up to over 100,000 litres going straight to the drain.

£100–£300 extra per year

On a metered water supply, a running toilet adds £100 to £300 a year to your bill in the South West Water region. Combined with the wasted hot water for partial flushes, the real cost is often higher.

You may not even hear it

Slow, silent leaks at the flush valve are common. The cistern keeps topping up just enough to stay full, with water trickling continuously into the bowl. The food colouring test (below) catches these.

Fixed in under an hour

Most running toilets are fixed by replacing a £30 flush valve washer. A plumber needs 30 to 60 minutes. DIY is realistic if you are comfortable working with simple mechanical parts.

Five-Step Diagnostic Check

Work through these in order. Most homeowners find the cause within five minutes.

Listen for trickling

After the cistern has filled and the fill valve has closed, listen near the bowl for trickling water. If you hear it, water is leaking from the cistern through the flush valve into the bowl.

Run the food colouring test

Put 5–10 drops of food colouring into the cistern. Wait 15 minutes without flushing. If colour appears in the bowl, the flush valve seal is leaking. This is the most reliable home test.

Lift the cistern lid

Look inside. If the water level is reaching the overflow tube and spilling into it, the fill valve is set too high or not shutting off — fill valve fault. If the water level is below the overflow but you still hear trickling, the flush valve is the problem.

Check the float and arm

In an older cistern with a float arm, see if the float is waterlogged (sitting low) or if the arm is bent. Either causes the fill valve to keep adding water past the correct level.

Inspect the flapper or syphon

In modern cisterns, the flush valve uses a flapper seal or a syphon. Look for warping, mineral build-up or splits. A quick clean sometimes solves the problem; a worn seal needs replacing.

Three Ways to Fix It

Pick the option that matches your DIY confidence and the age of the toilet.

DIY Flush Valve Washer

£5–£15

Time: 30–60 minutes

Skill: Confident DIYer

Turn off the isolation valve under the cistern
Flush to empty, then sponge out remaining water
Remove the old washer and fit the replacement
Refit and test for leaks

DIY Full Flush Valve Replacement

£25–£50

Time: 1–2 hours

Skill: Confident DIYer

More involved — cistern must come off the pan
Replace the entire flush valve assembly
Refit cistern with new bolts and seal
Risk of leaks if not refitted carefully

Plumber Callout

£80–£150

Time: 30–60 minutes

Skill: No DIY skills needed

Plumber diagnoses the exact cause
Carries parts to fix on the first visit
Tests for leaks and confirms the fix
Recommended if you are not confident or the toilet is older

When It Is Time to Call a Plumber

DIY is fine for simple fixes. These signs mean it is worth getting a professional in.

You are not confident turning off the isolation valve safely
The cistern is plastic and feels brittle (old units crack easily)
You have already replaced parts and it is still running
There is visible water on the floor around the base — likely a wax seal failure
The fill valve hisses or screams when filling — water pressure or valve fault
You smell sewage or notice a persistent smell after flushing

For the full repair cost breakdown, see our toilet repair service page .

Running Toilet FAQs

Need Help Fixing Your Toilet?

Browse our directory of local plumbers covering Exmouth and East Devon. A running toilet is usually a 30-minute job — call directly for a same-day quote.

Find a Plumber

See the full toilet repair service page for pricing on every fix. Blocked toilet instead? Read how to unblock a drain or browse blocked drains. Dripping tap? See how to fix a dripping tap. Hard water making it worse? Check your local water hardness. For wider pricing context see plumber costs.