Toilet running non-stop? The 3 usual culprits
A toilet that won't stop running is one of the most common plumbing jobs we get called out to across Hull. Sometimes it's a barely-audible hiss you only notice at night. Sometimes it's a proper waterfall down the back of the pan. Either way it's costing you money — a running toilet can waste 200 to 400 litres of water a day, and if you're on a meter that adds up fast.
The good news: it's nearly always one of three parts. Once you know which one, you know what you're dealing with. Here's how to spot each.
First — figure out where the water is going
Take the cistern lid off. It just lifts off — don't worry, nothing will explode. Now watch what's happening inside for 30 seconds. The three things you're looking at are:
- The flush valve — the big rubber flap or seal at the bottom middle of the cistern. This is what opens when you flush and lets water into the pan.
- The fill valve — the tall unit on one side, connected to the water supply pipe. This refills the cistern after a flush.
- The float — either a ball on an arm, or a cylindrical float sliding up a spindle. This tells the fill valve when to stop.
Now watch: is water dribbling from the top of the fill valve into the overflow tube in the middle? Or is the fill valve silent but the water level slowly dropping into the pan? Those two symptoms point at completely different problems.
Culprit 1: The flush valve seal
This is the most common one, especially in older toilets. The rubber flap or diaphragm seal at the bottom of the cistern hardens, distorts or gets grit under it. Water then slowly leaks from the cistern into the pan. The fill valve senses the drop and tops it up — so you hear the fill valve kicking in every few minutes even when nobody's used the toilet.
How to spot it: put a few drops of food colouring in the cistern water. Don't flush. Come back in 20 minutes. If the pan water is coloured, the flush valve is leaking.
The fix: a new flush valve seal or diaphragm. Most modern toilets it's a straightforward part swap once the cistern's drained. Older siphon-type flushes can be more involved because the whole siphon has to come out.
DIY-able? Maybe. Modern push-button toilets vary hugely by brand — the wrong part means a wasted trip to the merchants. If you're confident with a bit of research and can identify the model, have a go. If it's a wall-hung toilet or a concealed cistern, that's a plumber job.
Culprit 2: The fill valve
The fill valve is the bit that refills the cistern. When it fails, water either doesn't stop coming in (so it pours down the overflow tube in the middle), or it keeps trickling because the internal seal is worn.
How to spot it: water is visibly running down the internal overflow tube in the centre of the cistern, or dripping into the top of it. The fill valve is either constantly hissing, or making a soft trickling sound that never stops.
The fix: new fill valve. They come in a few standard fittings — bottom-entry and side-entry — and cost £10-£25. Fitting is straightforward once you know how the water isolates.
DIY-able? Yes, if there's a working isolation valve on the supply pipe, and you're comfortable with a spanner and a bit of PTFE tape. Watch out for cross-threading the plastic nuts — they only need to be hand-tight plus a nudge.
Culprit 3: The float
The float tells the fill valve when to shut off. If it's set too high, the water level rises above the overflow tube and pours down it forever. If the float itself has cracked and taken on water, it sinks and the fill valve never gets the signal to close.
How to spot it: water level is right up at or above the mark on the inside of the cistern. Overflow tube has water dribbling into it constantly. Wiggle the float — does it feel heavier on one side, or is there water inside?
The fix: often it's just an adjustment. On ball-and-arm floats, there's usually a screw at the pivot to lower the arm — turn it a couple of turns and the water level drops. On modern cylinder floats, there's a clip or thumbscrew that lets you slide the float down the shaft. If the float is cracked, it needs replacing — usually cheap and quick.
DIY-able? The adjustment, yes. Replacing a cracked float is usually simple too.
The one thing you should never ignore
If water is coming out of the external overflow pipe on your outside wall — that little pipe sticking out at first-floor level — sort it soon. It means one of the above has failed and the cistern is dumping water outside. It's telling you something's broken, but it's also soaking the wall below the pipe and can cause damp inside if it goes on long enough.
What we usually see in Hull
In older Hull housing stock — the terraces round Anlaby Road, Beverley Road, Holderness Road — we still see plenty of old-style siphon flushes. When they go it's usually the diaphragm at the top of the siphon splitting. It's a known fix and a common part.
In newer builds and refurbs it's ceramic-cartridge dual-flush units that go, and those are much more brand-specific. Getting the right part first time matters — otherwise you're back off to the merchants.
When to call a plumber
- Wall-hung or concealed cisterns — you need the frame apart to get at the workings.
- The isolation valve on the supply pipe doesn't turn, or there isn't one.
- You've replaced a part and it's still running.
- The cistern itself is cracked (rare but does happen).
- You honestly can't be bothered — fair enough, ring us.
What it usually costs
Rough guide only, parts extra. A standard fill valve or flush valve replacement on an accessible cistern is a quick visit. Concealed cisterns and wall-hung units take longer because of the panel work. We'll always give you a straight price before we start.
Full details on our toilet repair page.
Ring us if you'd rather just get it sorted
If you'd rather skip the food-colouring test and just have someone fix it, that's what we're here for. Water-side only, Hull-based, honest guide prices — give us a ring on the number at the top of the site.