How to fix a toilet that keeps running

How do you fix a toilet that keeps running?

🔧 Fixing a Toilet That Keeps Running

A running toilet is usually caused by an incorrectly adjusted fill valve, a worn inlet-valve diaphragm, or a leaking flush-valve seal allowing water to escape into the pan. Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials.

What skill level is needed to diagnose a running toilet?

Beginner to Intermediate — Estimated time: 30 minutes for diagnosis; 1–2 hours for valve or seal replacement

What tools do you need to repair a running toilet?

🔧 Tools Required

What replacement parts are needed for a running toilet?

🪵 Materials

Use only products carrying the required WaterMark certification. Flush-valve seals are not universal, so take the old seal or clear photographs and measurements to the plumbing supplier.

How do you work safely on a toilet cistern?

⚠️ Safety

🔒 Licensing: Plumbing work in Australia must be performed by a licensed plumber. This guide explains the process and helps you select the right tools and materials. Licensing and homeowner work limits vary; check NSW Fair Trading, the VIC VBA, QLD QBCC, or the WA Building Commission/Building and Energy before replacing valves or altering the water connection. Gas work requires a separate gas fitter licence.

Step-by-Step Guide

Step 1: 1️⃣ Confirm Where the Water Is Going

Remove the cistern lid carefully and place it flat on a towel. For push-button cisterns, the button surround may unscrew, or the lid may lift only after releasing clips—check the manufacturer’s instructions rather than forcing it.

Observe the cistern:

Dry the rear of the pan before checking for external leaks so condensation is not mistaken for a plumbing leak.

Step 2: 2️⃣ Perform a Dye Test

Allow the cistern to fill, then add several drops of food colouring to the cistern water. Do not flush.

Wait 10–20 minutes:

This test helps avoid replacing the wrong component.

Step 3: 3️⃣ Isolate and Drain the Cistern

Turn the toilet isolation valve clockwise until closed. Avoid forcing a stiff or corroded valve.

Flush the toilet and hold the button or lever down to remove as much water as possible. Catch the remaining water with a sponge, towel or wet vacuum.

If the cistern continues refilling after isolation, the isolation valve is passing water and requires licensed repair or replacement. Do not proceed with disconnecting the supply.

Step 4: 4️⃣ Check the Button, Lever and Flush Mechanism

Confirm that the push button, lever, cable or operating rods return freely after each flush.

For top-button cisterns:

Clean soap residue and mineral deposits from moving plastic parts with warm water and a soft brush. Do not apply oil or petroleum-based lubricant.

Temporarily operate the flush valve by hand. If it closes correctly without the button mechanism attached, the problem is probably button or rod adjustment rather than the valve itself.

Step 5: 5️⃣ Check and Adjust the Fill Valve

Restore the water briefly and observe the float. The valve should shut off before the water reaches the overflow opening.

Adjust the level using the valve’s screw, clip or float setting. The correct waterline is generally marked inside the cistern and should usually sit approximately 20–25 mm below the overflow, unless the manufacturer specifies otherwise.

Check for:

The small refill tube should be clipped above the overflow opening where required. It must not extend below the standing water level, as this can create siphoning and continuous refilling.

Turn the isolation valve off again before dismantling any component.

Step 6: 6️⃣ Clean or Replace the Inlet-Valve Diaphragm

Many Australian cistern inlet valves contain a rubber diaphragm or washer beneath the top cap. Grit or a worn diaphragm can prevent complete shut-off.

Following the valve manufacturer’s instructions:

Do not poke metal wire into small valve openings, as this can permanently damage the control orifice.

If the valve is old, brittle or has no available service kit, a complete WaterMark-certified fill valve is usually more reliable. Disconnecting or replacing the water inlet connection may be regulated plumbing work and should be completed by a licensed plumber.

Step 7: 7️⃣ Inspect the Flush-Valve Outlet Seal

With the cistern drained, remove the central flush-valve tower as directed by the manufacturer. Many units release with a partial anticlockwise turn, while others use retaining clips.

Inspect the rubber or silicone outlet seal underneath:

Apply only a very light film of potable-water-approved silicone grease if permitted by the manufacturer. Grease is not a remedy for a badly worn seal.

Reinstall the flush tower and confirm it locks securely and drops freely.

Step 8: 8️⃣ Reassemble and Test

Open the isolation valve slowly while watching the cistern. Check the inlet connection, valve body and cistern for leaks.

Allow the cistern to fill and confirm:

Repeat the food-colouring test and wait at least 10 minutes. Dry all external connections with paper towel; any new dampness indicates a leak requiring attention.

Step 9: 9️⃣ Replace the Complete Valve Only When Necessary

A complete valve may be required when:

Select a WaterMark-certified replacement that fits the cistern’s inlet location, outlet opening, height and button arrangement. Bottom-entry fill valves commonly connect to a 15 mm BSP toilet stop or connector, but compatibility must be confirmed rather than assumed.

Where the cistern must be removed, the supply connector changed, or the flush outlet disturbed, use a licensed plumber.

Step 10: 🔟 Know When to Call a Licensed Plumber

Arrange professional service if:

A licensed plumber can also check excessive supply pressure, which can shorten inlet-valve life and may require compliant pressure control under AS/NZS 3500.1.

Common Mistakes to Avoid

Pro Tips

💡 Mark the original water level and valve settings before adjustment so you can return to the starting position if needed.

💡 Photograph the valve, button and seal before visiting a plumbing supplier. Include brand markings and measurements.

💡 Place dry toilet paper against external joints during testing; it reveals small leaks more quickly than visual inspection.

💡 Exercise the isolation valve periodically, but never force it. A working local isolation valve allows leaks to be controlled quickly.

💡 If the toilet needs replacement, choose a minimum 4-star WELS dual-flush suite. A correctly operating 4.5/3 L model can significantly reduce household water use compared with older cisterns.

Recommended Tools

🔧 Recommended Tools