What to do if your toilet cistern is not filling or filling slowly

1. Check the shut-off valve

The shut-off valve is a little lever or tap that controls the water going into your toilet. You’ll usually spot it just behind or beside the loo. If it’s not fully open, the cistern won’t fill as it should. Turn it all the way anti-clockwise to get the water flowing again or, if you have a lever tap, make sure it’s in the open position.

2. Check for low water pressure

If your taps and shower have a weak flow, your toilet might also be slow to fill. This is often a sign of low water pressure. It can be easy to spot, but you should test your water pressure just to be sure.

If the pressure is regularly low, it’s best to call a plumber to check things over.

3. Check the fill valve for damage, blockages and debris

The fill valve is what allows water back into your cistern after you flush. If it’s clogged with dirt or limescale, the valve may not open properly. A gentle clean might solve the problem, but if it still doesn’t work or if the valve looks cracked or worn, then it may need replacing.

Fill valves are widely available and easy to buy online or from a plumbers’ merchant, but if you’re unsure, a plumber can take care of this quickly.

4. Adjust and clean the toilet float

The float inside the cistern rises with the water level and tells the valve when to close. If the float is stuck or set too low, your cistern won’t fill properly. Adjust its position to make sure it’s sitting at the right height.

If the float is damaged or has taken on water, it won’t rise as it should and will likely need replacing. Most modern floats are attached to the fill valve, so replacing one usually means replacing both parts together. Luckily, replacing a toilet float is something you can easily do at home.

5. Check the toilet flush mechanism for damage

The toilet flush mechanism is the rubber seal at the bottom of the cistern. If it’s damaged, water will leak into the toilet bowl and stop the tank from filling properly. Check to see if it’s warped, cracked, or not sitting tightly over the opening. If it looks worn, replacing it is a simple job.

6. Check if the toilet flush is stuck

Sometimes it’s something really simple. If the flush handle or button is stuck down, it can stop the fill valve from opening. Try gently lifting or releasing the flush mechanism and see if that allows the water to start flowing back in.

7. Remove bricks or other heavy objects from the toilet cistern

Although this is not common in recent times, in the past, people would sometimes place bricks or heavy objects in the cistern to save water. While this reduces the amount of water used per flush, it can also prevent the cistern from filling properly. If you find anything like this inside your tank, make sure to remove it.

8. Check the water supply line

If none of the earlier checks have worked, the problem could be with the water supply line itself. A blocked or kinked pipe can reduce the flow of water into the cistern. Take a look at the pipe that connects the toilet to the main supply. If it seems clogged or damaged, it may need replacing.

9. Call a professional plumber

If you’ve worked through these steps and your toilet cistern still isn’t filling properly, it’s best to call in one of our professional plumbers. If the problem keeps coming back, it could be a sign of a bigger issue in your plumbing system that’s best handled with the right tools and expert know-how.

Plumbing and drainage solutions you can count on

At HomeServe, we know how frustrating plumbing problems can be, but you don’t have to face them alone. With our Plumbing and Drainage Cover, you’ll have access to trusted engineers who can get your home back to normal quickly. Or, if you’d simply like a quick repair, book a plumbing job with Ding to get the job sorted fast.

Whether it’s a slow-filling toilet or something bigger, we’re here to help.