That faint hiss of water trickling into the bowl, long after the flush has finished, is more than an annoyance. A toilet that keeps running can waste hundreds of litres of water a day, push up your bill and keep you awake at night. The good news is that it is usually a simple, cheap fix once you know what is going on inside the cistern. Here’s why a toilet keeps running and how to put it right.
Why does my toilet keep running?
Everything that makes a toilet work sits inside the cistern, the tank behind or above the bowl. When you flush, water empties into the bowl and the cistern refills, ready for next time. A toilet that keeps running means water is either not stopping when the tank is full, or leaking out of the tank into the bowl so the tank never fills. Almost always, one of three parts is to blame for a toilet that keeps running.
1. The flapper or flush valve
At the bottom of the cistern is a seal, often a rubber flapper or a flush valve washer, that lifts when you flush and drops back to seal the tank. Over time this seal hardens, warps or collects limescale, so it no longer sits flush. Water then trickles past it into the bowl continuously, and the tank keeps topping up to replace it. This is the single most common reason a toilet keeps running.
2. The fill valve
The fill valve lets clean water back into the tank after a flush and shuts off when the water reaches the right level. If it is worn or set too high, it can keep letting water in, which escapes down the overflow. You may hear it running constantly or cutting in and out.
3. The float
The float tells the fill valve when to stop. If it is set too high, the water rises above the overflow and runs away continuously. If the float is damaged and waterlogged, it sinks and never signals the valve to shut off.
How to find the cause
If your toilet keeps running, take the lid off the cistern and look inside while the tank is full. A couple of quick checks will usually show you the problem:
- Is water running over the top of the overflow pipe? That points to the fill valve or the float set too high.
- Is the water level fine but you can still hear trickling? Put a few drops of food colouring in the tank and wait without flushing. If colour appears in the bowl, the flapper or flush valve seal is leaking.
- Is the float sitting low or waterlogged? It may need adjusting or replacing.
Simple fixes you can try
When a toilet keeps running, some fixes are easy to sort yourself.
- Adjust the float. You can lower most floats slightly so the water shuts off below the overflow. On modern valves this is a screw or clip; on older ball-floats you can gently bend the arm down.
- Clean the flapper or seal. Turn off the water at the isolation valve, drain the tank and wipe the seal and its seat. Limescale and grit often stop it sealing, and a clean can be enough.
- Check the chain or lift mechanism. If a chain is too short or tangled, it can hold the flapper slightly open. Give it a little slack.
If the seal is hard, cracked or warped, or the fill valve has worn out, you need to replace the part. These are inexpensive, but getting the right part and fitting it correctly, especially on older or concealed cisterns, is where many people come unstuck.
When to call a plumber
Call a professional if the toilet keeps running and won’t stop after cleaning and adjusting, if the cistern is concealed behind tiling or a wall unit, if the isolation valve is seized, or if there is a leak from the cistern rather than just inside it. A plumber will have the right parts on the van and can replace the flush valve or fill valve quickly, and sort any limescale or leak at the same time.
A running toilet is also a common job to roll into a visit for other small repairs, so if you have a list of bits and pieces, it makes sense to get them all done together.
Why it’s worth fixing quickly
A toilet that keeps running can waste a surprising amount of water, which shows up on a metered bill. The constant flow of water also speeds up limescale build-up on the parts, making the problem worse over time. Fixing it early keeps the repair small.
Fix a running toilet with CityPrime
If your toilet keeps running and a clean and adjust hasn’t solved it, our plumbing team in London can replace the flush or fill valve and stop the waste for good. We can also tackle any other small jobs on your list in the same visit through our handyman service. Call 020 3855 2692 or book online for a free quote.
Running toilet questions
Why does my toilet keep running after flushing?
A toilet keeps running usually because the flapper or flush valve seal at the bottom of the cistern no longer sits tight, so water trickles into the bowl. A worn fill valve or a float set too high can also cause it.
How do I know which part is faulty?
If water runs over the overflow, suspect the fill valve or float. If the level is fine but water still trickles, add food colouring to the tank: if it reaches the bowl without flushing, the seal is leaking.
Can I fix a running toilet myself?
Often, yes. Adjusting the float, cleaning the seal and freeing the chain solve many cases. If the seal or valve has worn out, you need to replace the part, which is cheap but fiddly to fit.
Does a running toilet waste much water?
Yes. A running toilet can waste hundreds of litres a day, which adds up quickly on a metered bill, so it is worth fixing promptly.
When should I call a plumber for a running toilet?
Call one if the running continues after cleaning and adjusting, the cistern is concealed, the isolation valve is seized, or the cistern itself is leaking.
