The rubber flapper (or, on dual-flush cisterns, the silicone seal on the flush cartridge) sits at the bottom of the tank and degrades over time. Once it stops sealing, water leaks continuously into the bowl — the classic cause of that on-and-off "phantom" refill you hear every few minutes. In older flats, hard-ish tap water hardens the seal, so this is the single most common fault we see.
If the float ball or cup is set too high, the fill valve never shuts off, causing water to constantly drain into the overflow tube.
If adjusting the float doesn't help, the fill valve's internal mechanism is likely worn — you'll often hear a constant hiss that never fully stops. This usually means a full valve replacement. It's a quick job for a plumber who carries common brand parts, but matching the right part is what stops the leak coming back.
How to Diagnose a Running Toilet in 5 Minutes
Before you call anyone, run the classic dye test. Lift the cistern lid, drop a few drops of food colouring (or a coloured pill) into the tank, and wait 15–20 minutes without flushing. If colour seeps into the bowl, your flapper or flush valve seal is leaking. If the tank water level keeps creeping up to the overflow tube and trickling away, the fill valve or float is the culprit. This one test tells you which of the three faults above you are dealing with.
Most Singapore HDB and condo units now use a dual-flush cistern (the two-button kind), where the old rubber flapper is replaced by a drop/flush valve cartridge with a silicone seal. These seals harden in our hard-ish tap water and over years of use, so a constant trickle is extremely common in flats more than 8–10 years old. Coupled cisterns (one-piece toilet bowls) and concealed cisterns behind a false wall use the same principle but are fiddlier to open.
When to DIY vs when to call a plumber
- DIY-friendly: adjusting the float height (bend the arm or turn the adjustment clip down), cleaning grit off the flapper seat, or swapping a like-for-like flapper on an older single-flush tank. Parts cost a few dollars at any hardware shop — always shut off the angle valve under the cistern first.
- Call a pro: dual-flush cartridge replacement (the part must match the brand — Geberit, Cotto, Baron, American Standard etc.), a cracked overflow tube, a fill valve that hammers or won't shut, or any leak from the tank-to-bowl gasket where water pools on the floor. Concealed cisterns almost always need a professional because the access panel and proprietary parts trip up DIY attempts.
A running toilet is not just an annoyance — a silent constant trickle can quietly waste hundreds of litres a day and push up your PUB water bill noticeably within one billing cycle. Fixing it early usually pays for itself.
Symptom → Cause → Fix (and Indicative Cost)
| What you notice |
Likely cause |
Typical fix & indicative price* |
| Intermittent "phantom" refill every few minutes |
Worn flapper / flush-valve seal leaking into bowl |
Replace flapper or cartridge seal — from S$80 |
| Continuous trickle into the overflow tube |
Float set too high / sticking |
Adjust or reseat float — often a quick callout from S$60 |
| Hissing fill valve that never fully stops |
Faulty / worn fill valve |
Replace fill valve — typically S$90–S$150 |
| Water on the floor behind the bowl |
Tank-to-bowl gasket / cracked cistern |
Reseal or replace parts — from S$120 |
*Indicative only. Dual-flush cartridges and brand-specific parts vary, so the final price is confirmed by our coordinator on WhatsApp or by the technician on site after assessment — never above the written quote.
Frequently Asked Questions
Can a running toilet really increase my PUB water bill that much?
Yes. A steady, silent trickle can waste hundreds of litres a day. Because the leak is constant and unnoticed, the extra usage stacks up across the whole billing cycle, so a single faulty flapper can add a visible jump to your bill before you realise anything is wrong.
Why does my dual-flush toilet keep running but there's no flapper to replace?
Dual-flush cisterns use a drop/flush valve cartridge with a silicone seal instead of an old-style flapper. Over years of use in Singapore's tap water the seal hardens or collects grit and stops sealing. The cartridge usually has to be replaced as a unit and matched to your cistern brand (Geberit, Cotto, Baron, American Standard, etc.).
How much does it cost to fix a running toilet in Singapore?
A simple float adjustment or flapper swap typically starts from S$80, while a full fill-valve or flush-valve replacement is usually S$90–S$150 depending on the part. These are indicative ranges — the exact figure is confirmed after the technician sees your cistern. See our
plumber cost guide for the full breakdown.
Should I just replace the whole toilet bowl instead?
Usually no. A running toilet is almost always an internal-parts problem, and replacing the flapper, fill valve or cartridge is far cheaper than a new bowl. Full replacement only makes sense if the cistern is cracked or the bowl is very old and you were already planning to upgrade.
Get it fixed properly
If the dye test points to a fill-valve or dual-flush cartridge problem, it is worth getting a plumber who carries common brand parts so the job is done in one visit. Explore our Singapore plumbing services, compare rates in the full price list, or message us on WhatsApp with a photo of your open cistern for a faster indicative quote.