A toilet that constantly runs is usually caused by a faulty fill valve, a worn flush valve seal, an incorrectly adjusted float, or a problem with the flush mechanism itself. While some issues can be fixed with a simple adjustment, others require replacement parts to prevent wasted water and higher bills.
400L/day
Water wasted
£80/month
Added bill cost
£75–£160
Typical repair cost
~1 hour
Typical repair time
Why This Happens
Understanding why your toilet is running starts with knowing how the cistern works. When you flush, the flush valve opens to release water into the pan, then closes so the cistern can refill. The fill valve tops up the water and shuts off when the float reaches the right level. If any part of this cycle fails, water keeps running. Here are the most common causes I see in homes across Woking and Surrey:
Worn Fill Valve
The fill valve (ballcock) controls water refilling the cistern after a flush. Over time, the internal diaphragm splits or perishes, so water never stops flowing — it trickles continuously into the overflow pipe and out through the external wall.
Damaged Flush Valve Seal
The flush valve seal (or flapper) is a rubber seal at the bottom of the cistern that lifts when you flush and closes to hold water in. When it warps, hardens, or collects limescale, it can't seal properly — water leaks from the cistern into the pan constantly.
Float Set Too High
The float controls when the fill valve shuts off. If it's adjusted too high, the water level in the cistern rises above the overflow pipe and continuously runs out through the overflow. A simple adjustment can fix this.
Limescale Build-Up
Surrey has very hard water. Limescale accumulates on the flush valve seat, fill valve diaphragm, and float mechanism, preventing clean seals and causing the valve to stick open or shut partially.
Faulty Push Button
On dual-flush toilets, the push-button actuator can stick or the internal linkage can snap, so the flush valve never fully closes after a flush. The button may feel spongy or not click properly.
Cracked Cistern Components
In older toilets, plastic cistern components become brittle and crack over years of thermal cycling. A cracked overflow tube or flush valve body can cause water to bypass the seal and run continuously.
Can You Fix It Yourself?
I'm always honest about what's safe to check yourself and when it's time to call a professional. Here's what homeowners can safely do — and when to stop.
Remove the cistern lid and check that the float moves freely — it should rise and fall smoothly without sticking.
Check the water level — it should sit about 2–3cm below the overflow pipe. If it's higher, the float needs adjusting down.
Put a few drops of food colouring in the cistern and wait 15 minutes. If colour appears in the bowl without flushing, the flush valve seal is leaking.
Check the push button — does it click and return smoothly? A stuck button means the flush valve isn't closing.
Don't attempt to replace a fill valve or flush valve assembly yourself unless you're confident isolating the water supply and reassembling the cistern internals correctly.
Don't force a stiff isolation valve or overtighten cistern fixing bolts — you can crack the porcelain or snap a valve, causing a flood.
If water is overflowing rapidly or leaking onto the floor, isolate the supply at the toilet isolation valve (behind the toilet) and call a plumber immediately.
When to call a plumber: If the simple checks above don't solve the problem, or if you're not comfortable dismantling the cistern internals, it's time to call a professional. A running toilet repair is quick and inexpensive — typically £75–£160 — and a botched DIY attempt can crack the porcelain or flood the bathroom, costing far more.
How I Repair Running Toilets
As the owner of The Maintenance Plumber, I regularly repair running toilets throughout Woking and the surrounding areas. In most cases, I can diagnose the fault within minutes of lifting the cistern lid — the sound, the water level, and the condition of the components tell me exactly what's wrong.
I carry replacement fill valves, flush valves, flapper seals, and syphon diaphragms in my van at all times, which means many repairs are completed during the first visit — no waiting for parts to be ordered, no second appointment. I isolate the water supply, replace the faulty component, descale any limescale build-up on the valve seat, and test the flush multiple times to confirm the problem is fully resolved.
Every repair comes with a fixed price quoted before I start, and a 12-month warranty on parts and labour. That's real experience — not just a marketing page.
Recent Example
A customer in Horsell contacted me because their toilet had been running continuously for several days. They'd noticed their water bill had increased and could hear a constant hissing from the cistern. When I lifted the lid, the water level was sitting above the overflow pipe and the fill valve was visibly not shutting off.
After isolating the supply, I removed the old fill valve and found the diaphragm had split — a common failure in hard water areas like Surrey. I replaced it with a new bottom-entry fill valve, adjusted the float to the correct water level, descaled the flush valve seat while I had access, and tested the flush multiple times.
The running stopped immediately. I estimated the faulty valve had been wasting approximately 400 litres per day — that's the equivalent of five full baths wasted every week. The customer was relieved to have it sorted before their next water bill arrived.
Response time
1 hour
Time on site
1.5 hours
Cost
£145
Warranty
12 months
Frequently Asked Questions
Can a running toilet increase my water bill?
Yes — significantly. A toilet with a faulty flush valve or fill valve can waste between 200 and 400 litres of water per day, which is up to 12,000 litres per month. On a metered supply, that adds £30–£80 to your water bill every month. The longer you leave it, the more it costs.
Is a running toilet an emergency?
It's not a burst-pipe emergency, but it should be treated as urgent. A running toilet wastes hundreds of litres of water per day and will increase your water bill significantly if left. If water is overflowing externally and could cause damage, or if the toilet is leaking onto the floor, isolate the supply and call us the same day.
Can I still use the toilet while it's running?
Yes, you can still flush and use the toilet. The running is caused by water leaking from the cistern into the pan (or out the overflow) — it doesn't affect the flush function. However, the constant water flow wastes water and should be repaired as soon as possible to avoid higher bills.
How long does a repair take?
Most running toilet repairs take between 30 minutes and 1 hour. A flush valve seal replacement takes about 30 minutes. A fill valve replacement takes 45–60 minutes. A full syphon replacement can take up to 75 minutes. Most repairs are completed in a single visit.
Do all running toilets need replacement parts?
Not always. If the float is simply adjusted too high, a quick adjustment costs nothing. If there's limescale on the flush valve seat, cleaning it may solve the problem. However, most running toilets are caused by a worn or perished component (fill valve diaphragm, flush valve seal, or syphon) that needs replacing. We carry common parts in the van.
How much does it cost to fix a running toilet in Woking?
Most running toilet repairs cost between £75 and £160 depending on which component needs replacing. Flush valve seal: £65–£90. Fill valve replacement: £90–£140. Full syphon replacement: £100–£160. We always give a fixed price before starting any work, so there are no surprises.
How do I know if my toilet is running?
The most obvious sign is a constant hissing or trickling sound from the cistern. You may also see water moving in the pan when no one has flushed. To confirm, put a few drops of food colouring into the cistern — if colour appears in the bowl within 15 minutes without flushing, the flush valve is leaking.
My toilet runs for a few seconds after flushing — is that normal?
A few seconds of running after flushing is normal as the cistern refills. If it runs for more than 2–3 minutes, or if you hear a continuous trickle between flushes, there's a fault that should be repaired. A properly functioning toilet should be completely silent within a minute of flushing.
Areas Covered
I provide toilet repairs across Woking, Horsell, Knaphill, West Byfleet, Pyrford, Addlestone, Chertsey, Guildford and the surrounding Surrey areas. If you're not sure whether I cover your area, just give me a call.
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