Dealing with a toilet cistern that isn’t filling properly can be frustrating. Whether it's taking ages to refill or not refilling at all, it’s a problem you need to fix quickly.
A malfunctioning cistern can lead to a toilet that won’t flush, so it's a priority to get it fixed.
But don’t worry; many of the issues causing this can be resolved with some basic troubleshooting. This guide will help you understand why your toilet cistern isn't filling and what you can do to fix it.
Why is my toilet cistern not refilling? 9 reasons and what to do
There are several reasons why your toilet cistern might not be refilling. Below are nine of the most common issues and how to fix them:
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Open the shut-off valve
Sometimes, the simplest solution is the correct one. The shut-off valve controls the flow of water to your toilet cistern. If it's not fully open, the cistern may not fill properly.
What to do:
- Locate the shut-off valve, usually found on the wall behind or beside the toilet.
- Turn the valve counterclockwise to ensure it is fully open. This should allow the water to flow freely into the cistern.
- Check if the cistern begins to fill. If it doesn’t, move on to the next step.
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Adjust the float ball
Float balls, or float cups, control the water level in the cistern. If it’s set too low, the cistern may not fill enough, or if it's stuck, it may not allow water to flow at all.
What to do:
- Switch the water supply to the toilet off by turning off the shut-off valve at the back of the toilet. If your toilet has a push or pull valve present, turn it clockwise or pull it out.
- Hold the lever down long enough to flush the toilet and remove most of the water.
- Remove the toilet cover and check if you have a float ball or a float cup.
- Gently lift the toilet float ball to see if water starts flowing into the cistern. If not, follow the next steps.
- If the fill valves have a float ball, you have to look for a screw where the float arm links to the fill valve. Turn this screw clockwise using a screwdriver to raise the water level in the toilet tank.
- Look for a long plastic screw attached to and alongside the float in a float cup. To raise the water level in your toilet tank, turn it clockwise with a screwdriver.
- Do not overtighten the screws while making the modifications. Turn the water supply on and off until the water level is half inches below the overflow tube.
- Before putting the lid back on the toilet tank, make sure the float ball or float cup moves freely and isn’t obstructed.
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Check for clogged water supply line
A clogged water supply line can reduce the flow of water into the cistern, causing it to fill slowly or not at all.
What to do:
- Turn off the shut-off valve and disconnect the supply line from the bottom of the toilet tank.
- Place a bucket under the line and turn the valve back on briefly to check for water flow.
- If the water flow is weak, the supply line might be clogged with debris. You may need to clean or replace it. If you're not confident doing this yourself, it might be time to contact a professional plumber.
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Readjust the toilet fill valve
The fill valves control the flow of water into the cistern after a flush. If they're not working properly, the cistern won’t fill.
What to do:
- Locate the fill valve on the left side of the cistern, where the float arm joins the valve.
- Check the adjustment screw on top of the fill valve. Turn it clockwise to increase the water level or counterclockwise to lower it. Use a flathead screwdriver.
- Ensure the fill valve is seated correctly and the refill tube is positioned over the overflow pipe.
If your toilet tank is equipped with adjustable cylinders, start by finding the fill valve on the left side of the tank. Next, press the float clip on the side of the valve.
Move it upward to allow more water into the tank, or slide it downward to reduce the water level.
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Replace faulty trip assembly
The trip assembly, which includes the handle, lift arm, and chain, controls the flushing mechanism. If it’s faulty, the cistern might not refill properly after a flush.
What to do:
- Inspect the trip assembly by lifting the toilet cover and checking the handle, lift arm, and chain.
- If any parts are broken or not working correctly, replace them with a new trip assembly kit.
- Make sure the chain has the correct amount of slack, allowing the flapper to open and close fully.
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Check for faulty toilet flapper
The flapper is a rubber seal at the bottom of the cistern that lifts when you flush, allowing water to flow into the toilet bowl. If the flapper is worn out or not sealing properly, the toilet's cistern won’t hold water.
What to do:
- Turn off the water supply and flush the toilet to empty the cistern.
- Inspect the flapper for wear or damage. If it looks worn or doesn’t seal tightly, it’s time to replace it.
- Install a new flapper by attaching it to the flush valve and connecting the chain to the trip assembly.
Minerals like calcium and debris in the water can sometimes accumulate under the toilet flapper and on the flush valve hole.
As a result, the flapper will not close properly, resulting in a running toilet and an empty toilet tank.
You can resolve this issue by running water through the flush valve and flapper.
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Replace toilet overflow tube
The overflow tube is a critical part of the toilet's inner workings, helping prevent excess water from spilling over. A cracked or broken overflow tube can lead to improper filling.
Luckily, replacing overflow tubes isn't overly difficult.
What to do:
- Check the overflow tube inside the cistern. If it’s cracked or broken, it will need to be replaced.
- To replace it, disconnect the tube from the flush valve and install a new one.
- Make sure the new overflow tube is properly positioned and securely connected.
Tip: Ensure the flow tube you purchase is the proper size. Alternatively, the entire flush valve can be replaced (which the overflow is a part of).
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Check for low water pressure
Low water pressure can cause your toilet cistern to fill slowly or not at all. This might be due to an issue with your home’s water supply.
What to do:
- Test the water pressure in other taps and fixtures in your home.
- If the water pressure is low throughout the house, you might need to contact your water supplier or a professional plumber to address the issue.
- If the low pressure is only affecting the toilet, check for kinks or leaks in the supply line and fix any issues.
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Remove bricks from toilet cistern
In the past, placing bricks or other heavy objects in toilet cisterns was a common method to save water. However, this can cause filling issues.
What to do:
- Remove any bricks or heavy objects from the toilet cistern.
- Check for any damage they may have caused to the internal components.
- Test the toilet to see if it fills properly after the objects have been removed.
When to call in a JustFix professional
While addressing a toilet cistern that isn’t filling can often be a DIY task, there are times when it’s best to bring in a professional.
If you’re having trouble fixing the issue or if the process seems too complicated, contact a qualified plumber from JustFix. Our experts provide top-notch service at affordable rates, ensuring your toilet system works properly and efficiently.
If your toilet continues to have issues despite your efforts, such as a persistently low water level or leaks, it could point to a more serious plumbing problem. Our nationwide team of Fixers can connect you with a trusted local plumber at a fair, fixed price.
When you book online with us, we’ll match you with a qualified plumber who can resolve your toilet cistern issues at a time that’s convenient for you.
