Toilet constantly running or trickling
A constantly running toilet is one of the most common plumbing niggles in UK homes, and the good news is it's usually quick and affordable to fix. The problem typically stems from two culprits: a worn flap valve at the bottom of the cistern, or a fill valve that's stopped shutting off properly. Both issues cause water to leak into the pan or overflow pipe, which not only wastes water and inflates your bills, but can also damage the cistern over time. This guide walks you through identifying which part is faulty and how to repair it yourself with basic tools and minimal fuss. Most fixes take under an hour and cost just a few quid in parts. If you're not confident working inside the cistern, or if the problem persists after trying these steps, it's worth calling a qualified plumber to rule out any underlying damage.
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
Remove the cistern lid and observe — check if pushing down the rubber flap stops the running.
If pressing the flap stops it: the flap valve is worn. Turn off the water supply, flush to empty, and replace the flap valve (£3–£8).
If water is running into the overflow pipe: the fill valve isn't shutting off. Try bending the ball arm downward slightly.
If adjusting doesn't fix it, replace the fill valve (£10–£20).
Prefer to have it done for you?
Find me an engineer →🛠 Tools & materials you may need
🔗 Some links above are affiliate links — if you buy through them we earn a small commission at no extra cost to you. This keeps the site free.
Was this guide helpful?
Frequently asked questions
How much water am I wasting with a constantly running toilet?
A leaking toilet can waste between 200 and 2,000 litres per day, depending on severity — that's easily enough to add £100+ to your annual water bill. Even a slow trickling sound indicates water loss, so it's worth tackling quickly rather than leaving it.
Is it safe to open the cistern lid myself?
Yes, absolutely. The cistern is simply a water storage tank with no electrical components or hazards inside. Just turn off the water supply at the stopcock before you start work, and remember to turn it back on once you've finished.
Can a running toilet cause damage if left unfixed?
Over time, constant water flow can erode the ceramic inside the pan and weaken the cistern seals, leading to leaks around the base. Fixing it promptly prevents more costly repairs down the line and keeps your water usage sensible.
What's the difference between a flap valve and a fill valve?
The flap valve (or flush valve) sits at the bottom of the cistern and releases water into the pan when you flush. The fill valve is at the top and refills the cistern after flushing — if either fails, water keeps running or trickling.
Do I need to replace the whole cistern if something breaks inside?
No — individual parts like the flap valve and fill valve are designed to be replaced separately and cost just a few pounds each. You'll only need a new cistern in rare cases where the ceramic itself has cracked or corroded beyond repair.
Where can I buy replacement cistern parts?
Most DIY stores, plumber's merchants, and online retailers stock universal flap valves and fill valves. Take a photo of your existing parts or the cistern model number when shopping, as there are a few different sizes and fitting types.