How to Fix a Stuck or Malfunctioning Flush Button on an External Cistern Toilet (by Capitan Farloc)

Is your toilet’s external flush button (CATIS type) getting stiff or pressing all the way down without triggering the flush? You’re not alone — these are very common issues! In this guide, I’ll walk you through how to identify the cause and fix the problem with just a few tools and some basic DIY skills. Even if you’re a beginner, clear steps and helpful illustrations will get your flush button working properly again in no time.

Introduction

Sometimes, the flush button on an external cistern toilet—such as the CATIS model, with a wall-mounted button and a porcelain tank positioned high up (commonly known as the “flush system”)—stops working properly. The most common issues are:

1. The button gets stuck when pressed and doesn’t return to its original position.
2. Pressing the button does not trigger the water flush.

This doesn’t always mean that the mechanism is broken or needs replacing. Here are some simple tips that can help you fix the problem yourself in most cases.

How Does the Toilet Flush System Work?

The mechanism is quite simple. The wall-mounted flush button acts as a pump, compressing air inside a tube that leads to the cistern. Once the air reaches the cistern, it pushes a piston, which then activates the flushing mechanism.
For a more detailed explanation of how this system works, I recommend reading the following article: 
How an External Cistern Toilet Flush System Works (by Capitan Farloc)

How to Remove the Toilet Flush Button

The most common issue involves the flush button itself, which may get stuck (as shown in the photo) or fail to activate the flushing system when pressed.
To fix this, you’ll need to unscrew the button’s retaining ring. In most cases, this can be done by firmly gripping the ring with one hand and turning it counterclockwise.

If the Retaining Ring is Stuck

If the retaining ring is too tight to unscrew by hand, I recommend using a Rubber Strap Wrench—a tool originally designed for removing oil filters in cars. It can be found in large hardware stores or online, such as on eBay.
This tool works by gripping the metal surface with a rubber strap, preventing scratches while allowing you to apply enough force to loosen the ring. In many cases, it proves to be an invaluable tool.

What’s Inside the Toilet Flush Button Mechanism?

Once the retaining ring is unscrewed, be careful—the return spring inside the button can easily pop out unexpectedly.

The Flush Button Mechanism

The mechanism is quite simple. In addition to the chrome retaining ring we removed and the return spring, it consists of a button connected to a metal cylinder that fits perfectly into its recessed housing in the wall.
This cylinder acts as a piston, and each time you press the button, it compresses air, directing it through a small tube to the upper cistern, where it activates the flushing system.

STEP 1 - Cleaning the Components

Malfunctions often occur due to dust mixing with the grease inside the mechanism. Over time, this buildup hardens, making it difficult for the button to return to its original position. Additionally, it can reduce the air seal, preventing proper compression.

To fix the issue, start by thoroughly cleaning all parts of the mechanism, removing any dirt or residue. I used alcohol for this, but you can also use non-aggressive degreasing detergents—just avoid descaling products.

The same cleaning process must also be carried out inside the recessed housing of the mechanism within the wall. Here, too, remove all dirt and residue using the same products used earlier.

STEP 2 - Lubricating the Components

To complete the repair, we need to apply grease to lubricate all the components.
I used silicone-based plumbing grease, which is commonly used for lubricating tap mechanisms. However, universal lithium or Teflon grease can also be used.

Applying the Grease

The grease should be applied both inside the recessed housing in the wall and on the outer surface of the cylindrical piston.
Its purpose is twofold: it lubricates the moving components, ensuring the button returns smoothly, and it improves the seal between the cylinder and piston, increasing the mechanism’s air compression efficiency.
Once all parts are properly greased (avoid using too much—a thin, even layer is sufficient), you can reassemble everything and test its functionality.

Thank you all for your time!
Luciano (Capitan Farloc)