How to Fix a Toilet Not Flushing
Last updated: 30 September 2026
Check the flush handle chain, adjust the chain length, check the flapper seal, and check the water level in the cistern.
Overview
A toilet that will not flush is a common and frustrating problem. This guide covers diagnosing and fixing a weak or failed flush.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- Remove the cistern lid and set it aside carefully on a flat surface. Ceramic lids are heavy and fragile so handle with both hands. Look inside the cistern to see the flush mechanism.
- Check the chain or link connecting the flush handle arm to the flapper valve at the bottom of the cistern. When the handle is pressed the chain lifts the flapper allowing water to rush into the bowl. If the chain is broken detached or too tight the toilet will not flush.
- If the chain is broken or missing replace it with a new one from a hardware store. Attach one end to the flush arm and the other to the flapper. Ensure the chain has about half an inch of slack when the flapper is closed. Too much slack means the chain does not lift the flapper enough. Too little slack causes the flapper to stay partially open and the toilet runs continuously.
- Check the flapper itself. The flapper is a rubber valve that seals the flush valve opening. Over time the rubber hardens warps or develops mineral deposits. A warped or hard flapper will not seal properly or lift correctly. Press down on the flapper with your finger to feel if it is soft and flexible.
- If the flapper is stiff or cracked it needs to be replaced. Turn off the water supply and flush the toilet to drain the cistern. Disconnect the old flapper from the overflow tube and install a new one of the same size. Reattach the chain and turn the water back on.
- Check the water level in the cistern. The water should reach the marked water line on the back of the cistern usually about one inch below the overflow pipe. If the water level is too low the flush will be weak. Adjust the float arm or the fill valve screw to raise the water level.
- If the water level is correct but the flush is still weak check the rim jets. The rim jets are small holes under the rim of the toilet bowl that direct water into the bowl during a flush. Limescale can block these holes and reduce the flush pressure. Use a mirror and a small wire to clear the holes.
- Turn the water supply back on and test the flush. Flush the toilet several times to confirm the repair. If the toilet flushes strongly and refills correctly the repair is complete.
- If the toilet still does not flush properly after all these checks the flush valve assembly may need replacing. This is the large plastic or brass mechanism at the bottom of the cistern. Replace it with a compatible unit of the same size. If you are unsure call a plumber.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| Handle moves but no flush | Broken chain or detached flapper | Replace the chain and ensure it has the correct amount of slack. Reattach the flapper if detached. |
| Weak flush | Low water level or blocked rim jets | Adjust the float to raise the water level. Clear blocked rim jets with a small wire. |
| Toilet runs continuously | Flapper not sealing or chain too tight | Adjust the chain to provide half an inch of slack. Replace a warped or hardened flapper. |
| No water in cistern | Fill valve not working or water supply off | Check the water supply valve is open. If the fill valve is faulty replace it. |
Frequently Asked Questions
Why will my toilet not flush properly?
A broken chain faulty flapper low water level or blocked rim jets are the most common causes. Check each of these one at a time to identify the problem.
Can I fix a toilet that will not flush myself?
Yes most flush problems are easy DIY fixes. You may need to replace the chain or the flapper. Both parts cost only a few pounds and can be fitted in minutes.
How do I adjust the water level in a toilet cistern?
Locate the float arm or fill valve inside the cistern. Bend the float arm slightly downwards to lower the water level or upwards to raise it. On modern fill valves turn the adjustment screw instead.
What is the flapper in a toilet?
The flapper is a rubber valve at the bottom of the cistern that seals the flush valve opening. When you press the handle the chain lifts the flapper allowing water to rush into the bowl. When released the flapper drops back and seals the opening.