A toilet that keeps running usually has one of two faults: a worn or limescaled seal on the flush valve, letting water trickle into the pan, or a fill valve set too high, so water spills into the overflow. A sticking float or push-button cable can cause either. It is rarely urgent and often a simple fix. The safe first step is to turn off the small isolation valve on the pipe feeding the cistern.
Is a running toilet urgent, and what should I do right now?
It is not dangerous, but it wastes water day and night, and on a water meter that shows up on your bill. Sort it within days, not weeks.
Most cisterns have an isolation valve on the feed pipe, just below or beside the cistern. A quarter turn with a flat screwdriver, so the slot sits across the pipe, stops the water. Open it again to refill before each flush. If there is no valve, or it will not turn, use the stopcock. If water reaches the floor, keep it away from sockets and shaver points.
Is the water going into the pan or into the overflow?
This one check tells you which part is at fault. Lift the cistern lid off carefully, as it breaks easily.
Look at the water level. If it is up to the top of the overflow tube (the open pipe in the middle of the flush valve) or above the marked water line, the fill valve is overfilling. If the level is below the overflow but water still trickles into the pan, the flush valve seal is leaking. A drip from an outside overflow pipe also points to the fill valve.
What are the most common causes?
In rough order of how often they turn up:
- Worn flush valve seal
- The rubber washer under the valve stops sealing, so water seeps into the pan.
- Limescale on the seal
- Leicester has hard water. Scale on the seal or its seat stops it closing.
- Fill valve set too high
- The cistern fills past the overflow and water runs constantly into the pan.
- Fill valve not shutting off
- A worn washer or scale inside lets water keep coming in.
- Float problems
- A float stuck on the cistern wall, jammed by scale, or waterlogged.
- Push-button cable
- A cable too tight, or a button that sticks, holds the valve slightly open.
How do I do the food colouring test?
It confirms a slow, invisible leak from the flush valve. Add a few drops of food colouring to the cistern, not the pan, and do not flush.
Wait about 30 minutes. If coloured water appears in the pan, the flush valve seal is letting water through. If the pan stays clear but the cistern keeps refilling, look at the fill valve and the water level instead. Flush afterwards to clear the colour.
What can I safely check or fix myself?
Quite a lot, with the isolation valve off and the cistern flushed empty.
- Lower the water level
- Most fill valves have an adjusting screw or clip on the float. Set it below the overflow.
- Free the float
- Make sure it moves up and down without touching the cistern or other parts.
- Check the button
- Press it and watch the valve drop fully. A sticking button may need its cable adjusting.
- Clean the flush valve seal
- Many valves twist or lift out. Wipe scale off the washer and seat.
- Fit a new seal
- Replacement washers are often available for common makes of flush valve.
When do I need a new flush valve, or a whole new cistern?
Most running toilets need a new part, not a new toilet. A new seal, fill valve or flush valve is usually the answer.
A new flush valve makes sense when the old one is cracked, badly scaled or has no spare parts. On a close-coupled toilet, where the cistern sits on the pan, the cistern often has to come off, with a new seal between the two. Many people call someone at this point, as a poorly seated cistern can leak at the back.
A new cistern is only needed if it is cracked or no parts fit. If an old cistern cannot be matched, a new toilet may be the tidier answer.
What will a plumber do, and when should I call one?
Call someone if the simple checks do not stop it, the cistern has to come off the pan, the isolation valve is seized or leaking, or water is getting onto the floor.
A plumber will check the water level, run the dye test, watch the flush and refill, and inspect the seals and cable. The fix is usually a new flush valve, fill valve or both, then testing the level. A seized isolation valve is worth replacing at the same time.
How do I stop it happening again?
Limescale is the main enemy in a hard-water area like Leicester, so keeping it down helps the valves last.
- Avoid in-cistern blocks
- Some chemicals can harden or swell rubber seals over time.
- Descale gently
- Use a product the valve maker says is suitable, not harsh acids.
- Listen for refilling
- A cistern that hisses or refills on its own is starting to leak.
- Check the isolation valve
- Turn it now and then so it does not seize.
Questions
Why does my toilet refill on its own every so often?
This is sometimes called a ghost flush. Water is seeping slowly past the flush valve seal, the level drops, and the fill valve tops it up. The food colouring test confirms it. Cleaning or replacing the seal usually stops it.
How much water does a running toilet waste?
It varies. A slow seep wastes a little; a fill valve running into the overflow can waste a lot every day. On a water meter it can add noticeably to your bill. Severn Trent may consider a leak allowance in some cases.
Why is water dripping from a pipe outside my house?
On older toilets and cold water tanks, the overflow pipe runs through the outside wall. A drip or steady flow from it usually means a fill valve is not shutting off, so the water level is too high. Lowering the float or replacing the valve fixes it.
Can I bend the float arm to fix it?
On an old-style ball valve with a metal arm, gently bending it down lowers the water level. Most modern fill valves have a screw or clip instead, so do not bend plastic arms. If the float is waterlogged, replace it or the whole valve.
Is a dual-flush toilet more likely to keep running?
Push-button dual-flush cisterns use a drop valve with a rubber seal, which can wear or scale up more readily than an old lever siphon. Most problems are easy to fix with a new seal or valve, and spares are widely available.
Can you fix a running toilet alongside other jobs?
Yes. Send a photo of the inside of the cistern, the button and the toilet, plus any other jobs. We reply within 24 hours with one fixed price for the lot, agreed before any work starts.