How to Stop a Running Toilet

A running toilet can waste up to 200 litres of water a day - that's serious money down the drain. The good news is that most running toilets are a 15-minute fix.

Why Toilets Keep Running

Water flows continuously because the tank never fills completely. This happens when:

• Flapper/flush valve doesn't seal - Water leaks into the bowl
• Float is set too high - Water overflows into the overflow tube
• Fill valve won't shut off - Keeps filling past the line
• Overflow tube is cracked - Water drains constantly

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Step 1: Identify the Problem

Take the lid off your cistern and watch what happens.

Test 1: The Dye Test

Add food colouring (or a dye tablet) to the cistern water. Wait 15 minutes without flushing. If colour appears in the bowl, your flapper or flush valve is leaking.

Test 2: Check the Water Level

The water level should sit about 25mm below the overflow tube. If water is flowing into the overflow tube, your float is set too high.

Test 3: Listen

If you hear the fill valve constantly cycling on and off, it's struggling to shut off properly.

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Fix 1: Adjust the Float

If water is overflowing into the overflow tube, the float needs lowering.

Ball Float (Old Style)

That plastic ball on an arm:

1. Bend the arm down slightly
2. Or turn the adjustment screw on the valve (if present)
3. Test - water should stop 25mm below overflow

Cup Float (Modern Style)

The float rides up and down the fill valve:

1. Find the adjustment screw or clip on the float
2. Turn screw clockwise or pinch clip and slide float down
3. Test and adjust until water stops at the right level

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Fix 2: Replace the Flapper

Flappers degrade over time - they get warped or mineral buildup stops them sealing.

What you'll need:

• New flapper (£5-£10, take old one to match)
• Towel

Steps:

1. Turn off water supply (valve behind toilet)
2. Flush to empty the tank
3. Unhook old flapper from overflow tube (usually just clips off)
4. Unclip chain from flush lever
5. Clip new flapper in place
6. Attach chain to lever (with a little slack)
7. Turn water back on and test

Pro tip: Clean the flush valve seat while you're there. Mineral buildup on the rim stops flappers sealing properly.

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Fix 3: Replace the Fill Valve

If adjusting the float doesn't work, the fill valve itself might be worn. They're cheap (£15-£25) and not hard to replace.

Steps:

1. Turn off water supply
2. Flush and sponge out remaining water
3. Disconnect water supply line from bottom of tank
4. Unscrew locknut under tank and remove old valve
5. Insert new valve, adjust height if needed
6. Tighten locknut (hand-tight plus quarter turn)
7. Connect water supply
8. Turn on and adjust float

Warning: Have a bucket and towels ready - water will come out when you disconnect the supply line.

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Fix 4: Check the Flush Valve Seal

On some toilets, the whole flush valve assembly needs replacing. This is a bigger job - the tank needs to come off.

If you've replaced the flapper and it still leaks, this might be needed. At this point, many people call a plumber.

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Dual Flush Toilets

Modern dual flush toilets have different mechanisms. The drop valve in the centre is usually the problem.

Common issues:

• Rubber seal worn on drop valve
• Debris caught under the seal
• Drop valve not sitting square

Fix: Twist and lift out the drop valve, clean or replace the seal, and reseat it.

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When to Call a Professional

Get help if:

• You've tried everything above - Might need new internals
• Tank is cracked - Replace the whole thing
• Hidden leak - If you suspect water is leaking elsewhere
• You're not comfortable - No shame in that

A running toilet usually takes me 15-30 minutes to fix. Most of the time it's a flapper or float adjustment.

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Can't stop the drip? We fix toilets across Exeter. Call 01392 964094 or get a quote.