Why Does My Toilet Keep Running?
Why Does My Toilet Keep Running? Causes, Quick Fixes & When to Call a Plumber
A toilet that won’t stop running is more than an irritation — it wastes water and adds to your bill. The good news is that most causes are simple and safe to check yourself. Below we explain the most common faults, easy DIY checks, and when it’s best to call a professional.
Fast check: Lift the cistern lid and watch what happens after a flush. If water keeps flowing into the overflow tube or you hear a constant hiss, you likely have a float level or fill valve issue. If the water in the bowl ripples every few minutes, the flapper may be leaking.
Most Common Reasons a Toilet Keeps Running
1) Worn or mis-seated flapper (flush valve seal)
The rubber flapper seals the opening at the bottom of the cistern. If it’s worn, warped, dirty, or the chain is snagging, water escapes into the bowl and the cistern keeps refilling.
- Signs: Bowl “ghost flushes”, need to jiggle the handle, flapper doesn’t sit flat.
- Quick fix: Turn water off, clean the seal and valve seat; ensure the chain has a little slack (about 6–12 mm); replace the flapper if perished.
2) Float set too high
If the float is set above the overflow tube, the cistern never reaches “full” and water spills into the overflow constantly.
- Signs: Continuous trickle into the overflow tube; water level close to the top.
- Quick fix: Lower the float using the adjustment screw or slider. Aim for a level roughly 25 mm (about an inch) below the top of the overflow.
3) Faulty or dirty fill valve (inlet valve)
Debris or wear in the fill valve can stop it from shutting off. Sometimes a gentle clean restores it; older valves may need replacing.
- Signs: Constant hissing sound; water entering even when the float is down.
- Quick fix: Isolate water, remove cap, rinse debris if the model allows; otherwise replace the valve (most modern valves are inexpensive and universal).
4) Refill tube pushed into the overflow
If the thin refill tube is inserted too far down the overflow, it can siphon water and keep the cistern topping up.
- Quick fix: Clip the refill tube so it discharges above the top of the overflow, not inside it.
5) Rough or scaled flush valve seat
Limescale or a nick on the valve seat stops the flapper sealing properly.
- Quick fix: With water off, wipe the seat clean; remove light scale with a non-scratch pad. Replace the flush valve if damaged.
Simple 5-Minute Diagnostic
- Turn the isolation valve clockwise to stop water (usually on the left under the cistern).
- Mark the water line, wait a few minutes. If the level drops, the flapper/seat is leaking.
- Open the valve and flush. If water pours into the overflow, float height/fill valve needs adjustment or replacement.
- Check the chain: too tight and the flapper can’t seal; too loose and it tangles.
- Ensure the refill tube is not pushed down the overflow.
Dye test: Add a few drops of food colouring to the cistern and wait 10–15 minutes without flushing. Colour appearing in the bowl indicates a leaking flapper/seat.
When to Call a Professional
- Concealed or wall-hung cisterns where access is limited.
- Dual-flush canister mechanisms that need specialist parts.
- Repeated running even after a new flapper or adjustments.
- Inlet valve won’t shut off or the isolation valve is seized.
- Any signs of leaks around the toilet base or water damage.
At P A Henery Ltd, we diagnose and fix running toilets quickly and cleanly — often on the first visit with common parts on hand.
Preventative Tips
- Operate the flush gently to prolong the chain and flapper life.
- Avoid drop-in tank tablets that can degrade rubber seals.
- If you live in a hard-water area, periodic descaling helps moving parts last longer.
- Have a quick look in the cistern during your annual plumbing or boiler service.
Need a Fast Toilet Repair?
Book a visit with our friendly, qualified engineers. We’ll identify the cause, replace any worn parts, and make sure everything is watertight before we leave.