Toilet Keeps Running? How to Fix It

A toilet that keeps running after flushing wastes water, makes annoying noise, and costs you money. The good news? Most running toilet problems are easy to fix yourself.

Understanding How Your Toilet Works

When you flush:

1. Handle lifts the flush valve (flapper or syphon)
2. Water rushes from cistern to bowl
3. Tank empties, triggering the fill valve
4. Tank refills until float reaches set level
5. Fill valve shuts off

A "running" toilet means water keeps flowing into the bowl or overflow.

Quick Diagnosis: What's Causing the Running?

Test 1: The Food Colouring Test

1. Put food colouring in the cistern
2. Wait 15 minutes without flushing
3. If colour appears in bowl = leaking flush valve

Test 2: Listen Carefully

• Constant flow = Fill valve not shutting off
• Intermittent refilling = Slow leak triggering refill
• Water going down overflow = Float set too high

Common Causes and Fixes

1. Faulty Flapper Valve (Most Common in UK)

What It Is: The rubber seal that lifts when you flush

Symptoms:

• Water trickles into bowl constantly
• Fails food colouring test
• Flapper looks worn, warped, or mineral-crusted

The Fix:

1. Turn off water supply (isolation valve behind toilet)
2. Flush to empty cistern
3. Unhook old flapper from overflow tube
4. Take flapper to hardware store to match
5. Install new flapper
6. Turn water on and test

Cost: £5-£15 for replacement flapper

2. Syphon Diaphragm Failure (Traditional UK Toilets)

What It Is: Many UK toilets use a syphon mechanism rather than flappers

Symptoms:

• Weak or incomplete flush
• Water continues running after flush
• Need to hold handle down to flush

The Fix:

1. Turn off water and empty cistern
2. Remove syphon mechanism
3. Replace diaphragm washer
4. Reassemble

Cost: £8-£20 for diaphragm kit

3. Fill Valve Stuck Open

What It Is: The fill valve controls water entering the cistern

Symptoms:

• Constant water flow into cistern
• Water going down overflow pipe
• Adjusting float doesn't help

The Fix (try first):

1. Turn water off and on quickly to flush debris
2. Clean around the valve seal
3. Check for debris blocking valve

If That Fails: Replace the fill valve (£15-£30 for valve)

4. Float Set Too High

What It Is: Float tells fill valve when to stop

Symptoms:

• Water overflowing into overflow tube
• Toilet "refills" periodically

The Fix:

• Ball cock float: Bend arm downward slightly
• Cup float: Adjust screw on side of valve
• Electronic valve: Check settings button

Goal: Water level should be 2-3cm below overflow

5. Flush Valve Seal Degraded

Symptoms:

• Water leaks between cistern and bowl
• Running only happens after flushing
• Visible wear on large seal at cistern base

The Fix:

1. Turn off water, empty cistern
2. Remove cistern from bowl (requires two-person lift)
3. Replace large washer between cistern and bowl
4. Refasten and test

Cost: £5-£15 for close-coupling kit

When to Replace vs Repair

Repair If:

• Toilet is relatively modern (< 15 years)
• Only one component is faulty
• Parts are readily available

Replace If:

• Multiple components failing
• Toilet is very old with unavailable parts
• Cracks in porcelain
• Considering a water-saving upgrade

Water and Money Wasted by Running Toilets

Leak Severity	Water Wasted	Annual Cost*
Slight drip	50 litres/day	~£50
Visible trickle	200 litres/day	~£200
Constant flow	500+ litres/day	~£500+

*Based on average Scottish water rates

Professional Toilet Repair Costs

Service	Typical Cost
Fill valve replacement	£75-£120
Syphon replacement	£80-£130
Full cistern internals	£100-£150
New toilet installation	£180-£300

Get Your Toilet Fixed

If DIY isn't your thing or the problem persists, our Glasgow plumbers can fix your running toilet quickly.

Plumbers Glasgow Ltd:

• Call: +44 141 468 9930
• Same-day toilet repairs
• Fixed price quotes
• All parts included

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Related Services:

• Plumber Glasgow
• Toilet Installation Glasgow
• Bathroom Plumbing Glasgow

Related Articles:

• How to Fix a Dripping Tap
• Blocked Toilet Guide