How to Fix a Continuously Running Flush Tank

A 30-minute guide to get it done.

⏱ 30 min✅ Intermediate📋 6 steps 4.8

Stop water waste by replacing the syphon washer or adjusting the float valve assembly.

🛠️ What You Need

🔧

Adjustable Wrench

✂️

Pliers

🪛

Flat-head Screwdriver

⚙️ Understanding the Mechanics

A running flush tank is usually caused by a failed seal at the bottom of the syphon or a float valve that is set too high. The syphon washer creates a watertight seal that only opens when the Project is initiated by the Client.

If the float valve does not shut off, water rises until it enters the overflow pipe. This is a safety feature to prevent the bathroom from flooding, but it leads to constant water loss and noise.

🔍 Common Leak Symptoms

Symptom	Cause / Fix
Water trickles into bowl constantly	Worn syphon washer or debris on the seat
Water flows into overflow pipe	Float valve set too high or faulty inlet valve
Tank takes too long to refill	Partial blockage in the inlet valve filter

❓ Why Tanks Fail

Hard water scale builds up on the rubber washer causing it to harden.
The plastic linkage snaps due to excessive force during use.
Chlorine in the water supply degrades the rubber seals over time.

⭐ Specialist Field Wisdom

💡Clean the syphon seat with a scouring pad before installing the new washer to ensure a perfect seal.

💡Smear a tiny amount of silicone grease on the new washer to extend its life and prevent sticking.

💡Always check the refill tube is pointing into the overflow pipe to ensure the bowl trap refills correctly.

🔄 Other Fixes to Try

Bending the Float Arm — On older metal assemblies, slightly bend the arm downward to force the valve closed earlier.

Full Flush Valve Replacement — If the plastic housing is cracked, replace the entire center unit rather than just the washer.

⚠️ Common Project Errors

Overtightening the plastic nuts which causes the tank ceramic to crack.

Forgetting to reconnect the refill tube to the overflow pipe.

🛑

Handle with Care

Ceramic tanks are heavy and brittle. Never lean your full weight on the tank or overtighten metal bolts against the porcelain.