Short answer: Most household plumbing faults worth fixing yourself come down to a short list of worn rubber and plastic parts — and the symptom tells you which one before you buy anything. A toilet that refills by itself is leaking from its tank into the bowl; a tap or faucet that still drips after a new washer is telling you the washer was never the whole story. Find your symptom in the table below, run the free test that confirms it, then follow the guide that matches.
Who this page is for: Homeowners and renters in the US and UK with a running toilet or a dripping tap/faucet · DIY level: Diagnosis is easy and free; the fixes in these guides are beginner-level with the water turned off — each guide marks where that stops being true · Cost: Every diagnosis on this page costs $0 / £0; the parts involved are among the cheapest in the house
Safety box — read this before any plumbing guide on this site
Learn where your water turns off before you need it: the isolation valve behind the toilet or under the sink for the fixture you are working on, and the main stopcock (UK) or main shut-off valve (US) for everything else. If an isolation valve is seized, crusted, or starts to leak when you touch it, stop — a forced valve is how a $10 fix becomes a flood. Keep water away from electrics: if a leak is anywhere near sockets, outlets, or a consumer unit / breaker panel, isolate the power or call a professional. Nothing in these guides involves gas, boilers, or mains electrical work.
How diagnosis works on this page
Plumbing parts are cheap, but buying the wrong one three times is not — and the most common way that happens is skipping the diagnosis and going straight to the part someone on a forum replaced for a similar symptom. A toilet that runs every few minutes, a toilet that runs constantly, and a toilet with a silent trickle into the pan are three different faults with three different fixes, and they are told apart by two free tests, not by opening the parts catalogue.
Every guide here follows the same order:
- Name the symptom exactly. When does it happen, how often, and can you see water moving anywhere it should not be?
- Run the confirming test. The dye test for toilets, the tap-type check for drips. Two minutes, no tools, and the result decides the part.
- Fix in order. Cheapest and most likely first, with the “if that didn’t fix it” cause already written into the same guide — because a failed first fix is information, not bad luck.
Symptom → likely cause: the plumbing overview table
| What you notice | Most likely cause | Where to start |
|---|---|---|
| Toilet refills by itself every few minutes, then stops | Water leaking from tank to bowl past a worn flapper (US) / flush seal (UK) — a “phantom flush” | Phantom flush guide |
| Toilet runs constantly and never fully stops | Fill level too high (water spilling into the overflow tube) or a fill valve that will not shut off | Phantom flush guide — fill-valve section |
| Silent trickle of water down the back of the toilet pan/bowl | Perished drop-valve seal on a UK dual-flush cistern | Water trickling into the pan guide |
| Damp or dripping at the joint between cistern and pan | Close-coupled washer / donut seal at the joint — a different leak from the one above | Water trickling into the pan guide — joint section |
| Toilet double-flushes or needs the handle held down | Chain slack, flapper weight, or flush volume setting — not a leak | Phantom flush guide — symptom table |
| Faucet still drips after fitting a new washer (US) | Scored valve seat underneath the washer, or the wrong cartridge — in that order | Faucet still dripping guide |
| Tap still drips after changing the washer (UK) | The tap may not have a washer at all — modern quarter-turn taps use a ceramic-disc cartridge | Tap still dripping guide |
| Drip gets worse, or the tap is stiff and gritty to turn | Cartridge wear or limescale damage — the soak-or-replace decision | Tap still dripping guide |
Two honest notes on the table. First, a leak inside the toilet (tank to bowl) wastes water but does not damage the house, so you can diagnose it calmly and in order. Second, any leak you can see outside the fixture — at a supply line, a valve, or a joint — outranks everything else on this page: water off first, diagnosis second.
Start with your symptom — the plumbing guides
Toilets that won’t stop
Toilet Keeps Running Every Few Minutes? It’s a Phantom Flush — Find the Leak in 2 Minutes
Start here if: your toilet (US-style tank with a flapper) tops itself up every few minutes, day and night, nobody near it. The guide opens with the two checks that split this fault in half — the waterline check at the overflow tube, then the dye test: food colouring in the tank, wait 15 minutes, and coloured water in the bowl proves the flapper is leaking past its seal. From there it is the flapper swap (about $5–$15, roughly 10 minutes, no tools), the chain-slack detail that causes half of all repeat phantom flushes, and the fill-valve section for the toilet that runs constantly instead. Renters get a straight note on what is yours to swap and what is the landlord’s.
Water Trickling Into the Toilet Pan? The Dual-Flush Seal Is the Usual Culprit (UK)
Start here if: your UK dual-flush toilet has a silent, constant trickle running down the back of the pan — no noise, no refill cycle, just water moving that should not be. US-centric advice barely covers this fault because the hardware is different: a drop valve sealing against a seat at the base of the cistern, and a perished rubber seal is the usual cause. The guide separates the three leaks that get confused with each other — trickle into the pan, leak at the cistern-to-pan joint, and external drips — then walks the fix: isolate, drain, remove the drop valve, clean the seat, fit the correct seal for your valve brand, and test. The part costs a few pounds; the diagnosis is the valuable bit, and it is free.
Taps and faucets that still drip after a washer
Faucet Still Dripping After a New Washer? Check the Valve Seat Next
Start here if: you did the obvious fix (US compression faucet, new washer) and the drip is still there — this guide is written for the second attempt, which is exactly where the big how-to sites stop. A new washer seals against a metal valve seat, and if that seat is scored or corroded, no washer will ever seal — the guide shows how to inspect the seat, dress it with a reseating tool or replace it, and how to tell when the real fault is the cartridge or its O-rings instead. It finishes with the honest economics: the point at which replacing the faucet beats repairing it again.
Tap Still Dripping After Changing the Washer? It Might Be a Ceramic-Disc Cartridge (UK)
Start here if: your UK tap drips despite a washer change — or despite your best efforts to find a washer at all. The lead diagnosis is the one the retailers skip: most modern UK taps are quarter-turn ceramic-disc designs, and there is no washer inside to change. The guide starts with the 10-second tap-type identification test, then the cartridge job itself, including the step everyone skips — measuring the cartridge spline and size before ordering, because “looks about right” is how the wrong cartridge gets bought twice. A limescale soak option for borderline cartridges in hard-water areas comes before the replacement verdict.
The two tests that decide most of these faults
The dye test (toilets, 2 minutes of work). Drops of food colouring in the tank or cistern, do not flush, wait 15 minutes, look in the bowl. Colour in the bowl = water is passing the flush seal/flapper — the leak is found and the part is named. Clear bowl = the flush seal is fine and you look at the fill level and fill valve instead. One test, and the toilet parts shelf stops being a guessing game.
The tap-type test (taps, 10 seconds). Turn the tap fully on and count the rotation. A handle that turns a quarter or half turn and stops is a ceramic-disc cartridge tap. A handle that keeps winding through several full turns is a traditional washer tap. This single observation decides which of the two drip guides applies to you — and it explains a great many “changed the washer, still dripping” mysteries, because on a cartridge tap there was never a washer causing the drip.
When plumbing is NOT a DIY job
Diagnosis is nearly always safe; some situations are not a learning opportunity. Turn the water off and call a licensed plumber (US) or a reputable plumber (UK) if:
- The fixture’s isolation valve is seized or starts leaking when touched. Forcing it can flood the room; a plumber swaps it under controlled conditions.
- A supply line, flexi hose, or fitting is split, bulging, or spraying. Water off at the main stopcock / main shut-off first — then call.
- The leak is at the soil pipe or waste (UK: the large pipe at the back of the toilet; US: the closet flange and drain), or you can smell sewage. That is drainage, not the water-supply faults this page covers.
- Water has reached electrics — sockets/outlets, light fittings, or the consumer unit / breaker panel — or a ceiling below is staining or bulging.
- You are a renter and the fault is in the fixture itself rather than a consumable seal or flapper. Note the diagnosis (it makes the landlord’s plumber faster), then report it.
US / UK term box
Reading from the other side of the Atlantic? Same pipes, different words — and on this cluster the hardware genuinely differs, which is why Articles 7 and 8 are separate guides rather than one translated page.
- Faucet (US) = tap (UK). Same fixture.
- Tank (US) = cistern (UK) — the water box behind or above the toilet.
- Flapper (US) = the rubber seal on a US flush valve. UK dual-flush toilets use a drop valve and seal instead — a different part doing the same job, which is why the trickle-into-pan fault has its own UK guide.
- Shut-off / isolation valve — same part both sides; the main one is the stopcock (UK) or main shut-off valve (US).
- Supply line (US) = flexi hose / service pipe (UK) — the braided or copper feed to the fixture.
- Valve seat (US compression faucets) = the brass seat under a traditional UK tap washer — same sealing principle, which is why a scored seat defeats a new washer in both countries.
FAQs
Is a phantom flush wasting much water?
Enough to matter: the tank leaks into the bowl and the fill valve tops it up every few minutes, around the clock, and the toilet is usually the largest single water user in the house. The exact amount depends on the leak, which is why the dye test comes first — a flapper costs about $5–$15 and ten minutes once the diagnosis is certain, so the fix is almost always worth doing promptly.
Why does my toilet run constantly instead of every few minutes?
A constant run usually means water is spilling into the overflow tube because the fill level is set too high, or the fill valve is no longer shutting off at all. That is a different fault from the flapper leak behind a phantom flush, and it is checked first at the waterline: the level should sit roughly an inch (2–3 cm) below the top of the overflow tube. The phantom flush guide covers both patterns and their order.
I changed the washer and the tap still drips. What did I do wrong?
Probably nothing — the diagnosis was incomplete. A new washer seals against a metal seat, and a scored or pitted seat lets water past a perfect washer; alternatively, the tap is a ceramic-disc design with no washer in it at all. Run the 10-second tap-type test above, then follow the matching guide: US valve seat (/faucet-still-dripping-after-washer/) or UK ceramic disc (/tap-still-dripping-ceramic-disc/).
Do I need a plumber to change a flapper or a flush seal?
In most cases, no — both are designed to be replaceable with the water off and no special tools, and the guides here walk them step by step. The exceptions are the stop conditions above: a seized isolation valve, a leak at a supply fitting, or anything outside the tank/cistern itself. Knowing the diagnosis also means that if you do call a plumber, you can describe the exact fault — which makes the visit shorter.
The trickle is inside the toilet pan, not on the floor. Can it wait?
It will not damage the house the way an external leak can, because the water goes down the drain — but it runs constantly, it is water you are paying for (metered homes especially), and the seal only gets worse. It is a calm, planned fix rather than an emergency: diagnose with the tests in the trickling into the pan guide (/water-trickling-into-toilet-pan/), order the seal for your exact valve brand, and swap it with the water off.
FaultToFix plumbing guides are written symptom-first: diagnosis before fix, cheapest check first, and a clear line where DIY stops. Turn the water off before removing any part.
Last updated: 26 October 2026