How to Stop a Running Toilet (UK DIY Guide)
A constantly running toilet can waste hundreds of litres of water per day and increase your water bill. In most cases, the problem is caused by a faulty flush valve, worn seal or incorrectly adjusted fill valve.
This step-by-step UK DIY guide explains how to stop a running toilet safely and when you should call a professional.
Tools You’ll Need
- Adjustable spanner
- Screwdriver
- Replacement flush valve seal (if needed)
- Replacement fill valve (if needed)
- Sponge or small container
Step 1: Remove the Cistern Lid
Carefully lift off the cistern lid and place it somewhere safe.
Flush the toilet and observe what happens inside.
Step 2: Check the Flush Valve Seal
Most running toilets are caused by a worn rubber seal at the base of the flush valve.
Turn off the water supply using the isolation valve.
Flush the toilet to empty the cistern.
Remove the flush valve mechanism and inspect the rubber seal.
If worn or damaged, replace it.
Step 3: Adjust the Fill Valve
If water is flowing into the overflow pipe, the fill valve may be set too high.
Locate the adjustment screw or float arm.
Lower the float slightly so the water stops below the overflow pipe.
Turn water back on and test.
Step 4: Replace the Fill Valve (If Necessary)
If adjusting doesn’t work:
Turn off the water supply.
Disconnect the water inlet.
Remove the old fill valve.
Install the new one following manufacturer instructions.
Reconnect and test.
Common Mistakes to Avoid
- Not turning off water supply
- Overtightening plastic fittings
- Ignoring a cracked cistern
- Using incorrect replacement parts
Take photos before removing components.
When to Call a Professional
You should seek professional help if:
- The cistern is cracked
- The toilet is leaking at the base
- The water supply valve is faulty
- The problem continues after part replacement
- You’re unsure how to isolate the water
For typical repair pricing, see our Toilet Repair Cost Guide.