Toilet constantly running

What is your toilet doing?

Use the two water-level clues only if the cistern interior is already safely visible. You do not need to remove a lid, button or panel to use the rest of this guide.

Is your toilet running between flushes?

This guide is for water that keeps entering the toilet bowl after the flush has finished, or a cistern that starts refilling when nobody has used it. You might see a fine trickle at the back of the pan, hear the fill valve running, or notice that the sound stops and starts.

First, separate water going into the bowl from water escaping outside the toilet. A wet floor, a leaking connection or a bowl whose water level is rising needs a different assessment. Do not follow an internal-cistern check simply because both problems are described as a “leaking toilet”.

Why does a toilet keep running?

The two routes below explain running water in a cistern with a fill valve, flush valve and overflow. They help narrow the investigation; more than one fault can be present.

A toilet that refills by itself may be replacing water lost from the cistern. That explains why a leak can sound like an intermittent filling problem. It still does not establish which component needs attention.

The outlet-seal explanation applies to flush-valve designs. A siphon cistern has a different mechanism: do not buy a flush-valve seal just because your toilet keeps running.

Start with checks that do not need tools

1. Look for water outside the toilet first

   If water is escaping onto the floor, or you cannot tell where it is coming from, stop this check and use the urgency guidance below. Water near electrical fittings takes priority over investigating the cistern.

2. Look and listen between flushes

   After the toilet has finished its normal refill, look for water continuing down the back of the pan. Note whether the sound is continuous or whether the cistern refills again later.

3. Use a paper check if a small trickle is hard to see

   NI Water describes waiting 30 minutes after a flush, drying the back of the pan with toilet paper, then placing a fresh dry sheet there. Leave it for a few hours or overnight without flushing. Wet or torn paper indicates water passing into the pan. This identifies a leak, not the failed part.

You need toilet paper and enough light to see the back of the pan. Choose a time when nobody will flush during the test. If the paper stays dry but the cistern later refills by itself, record that too: one dry check does not rule out an intermittent fault.

Keep these checks observational. If you cannot see the mechanism without dismantling it, the pan check and a description of the sound are enough to start a conversation with a plumber.

Which part might be faulty?

Look for a model name in paperwork or on parts that are already visible. A photograph can help a plumber or manufacturer identify the valve. Give both the toilet brand and any valve markings: the name on the ceramic pan may not identify the internal fittings.

Can you fix a running toilet yourself?

Yes, some running-toilet faults can be fixed without replacing a valve or booking a plumber. A dirty flush-valve seal may need cleaning; a damaged seal may need replacement. The useful distinction is between a simple action you can complete safely and a repair that depends on the exact mechanism.

Do not force a stiff stop valve or operate a valve you cannot identify. A shared valve can affect other homes. If you cannot safely stop the correct supply, ask a plumber before maintenance.

This page covers checks and repair decisions, rather than a universal valve-replacement procedure. For any repair, the final checks need to confirm that the running has stopped and no new external leak has appeared.

• Before choosing a repair, note whether the running is constant or the cistern refills intermittently, and whether water reaches the overflow if it is already safely visible.
• Find the mechanism name in existing paperwork or visible markings; do not buy a seal based only on the name on the ceramic pan.
• Read the complete matching procedure before starting. If access, the correct water isolation or reassembly is unclear, get clarification from the manufacturer or a plumber first.
• After a repair, check that the refill finishes, the between-flush trickle has stopped and no water is escaping outside the toilet. An intermittent fault needs checking again when it would normally recur.

How urgently should it be repaired?

The next step depends on where the water is going. Use the situations below to decide when to arrange a repair or seek urgent help.

What might a running-toilet repair cost?

A small replacement part can cost much less than the visit to diagnose and fit it. Compare the complete quote: the right part, access to the cistern, labour, VAT and any attendance or urgent-call charge. The published examples below show how those charges differ.

These are published examples checked on 28 September 2026, not verified invoices or a UK average. The older tariffs are labelled so you can see their limits. We have not combined them into a national price range or assumed that unspecified charges are included.

What the parts alone can cost

These Screwfix observations are from 26 September 2026 and include VAT, but not fitting or delivery. Each is a particular product, not a recommendation for your cistern. Confirm the model and current price before ordering.

Ask whether the repair quote already includes attendance before adding a call-out charge. Evening, weekend and same-day tariffs can differ. Confirm the final price basis before booking.

• Does the quote include diagnosis, the correct part, labour and VAT?
• Is access to a concealed cistern included?
• What is charged if another visit or a different part is needed?
• Does urgent or out-of-hours attendance change the price?

When it is time to get professional help

Call a plumber if you cannot identify the water route, cannot safely isolate the supply, would need to dismantle an unfamiliar concealed system, or have not resolved the problem after following the correct model instructions. Get urgent help for an uncontrolled external leak. A water-affected electrical system also needs appropriate electrical expertise.

Common questions