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How to fix a toilet flush

Keeping your toilet flush in good working order makes environmental and economic sense because it saves you water and money. Toilet flushing accounts for 20% of domestic water consumption, so a simple leak soon becomes a bottomless pit for your hard-earned wedge. That's why you need to act quickly if your flush develops a fault. The job is within anyone's ability. Just follow our advice to identify the cause and solve the problem.
Troubleshooting cistern problems

Cisterns can develop two types of problem:

  • The cistern takes too long to fill
  • Water runs into the bowl all the time

You need to find the cause of the problem before you can make a repair. Removing the cistern cover is the first step to seeing what the trouble is.

1. Remove the cistern cover

Unless your cistern is fitted with a cable to let you to work inside without removing the flushing control, you’ll have to remove the flushing control and the cistern cover. If the flushing control is a knob type, simply unscrew it.

Button type flushing controls can be removed in two ways, depending on model. Unscrew the ring around the button Or lift up the button (or buttons in the case of a double-button control) using a small screwdriver, just enough to get to the control retaining screw and unscrew it. Lift off the cistern cover and place it gently on the floor.

2. Find the faulty part

If the cistern takes a long time to fill:

  • The problem lies with the filling mechanism.
  • The float valve is probably damaged or fouled with limescale.

If water runs out of the overflow:

  • Too much water is entering the cistern. The float is badly adjusted, faulty or fouled with limescale. It’s failing to shut off the water supply when the cistern is full.

If water is leaking from the bottom of the cistern:

  • The flushing mechanism is faulty. Either the plug or one of the seals is worn or fouled with limescale.
Repairing the float valve seal

Close the water supply valve, then flush the toilet.

Unscrew the float mechanism from the water supply valve outside the cistern using adjustable pliers. Remove the float mechanism from inside the cistern and open the valve to get at the seal. Grip the seal and pull it gently out of the float valve. This seal is normally made of black rubber.

Clean the seal with a cloth and see whether it’s fouled with limescale or broken.

  • If it’s only fouled with limescale, soak it in vinegar.
  • If it’s broken, change it.

Fit the descaled or new seal in the float valve. Rinse and dry the parts. Screw the two parts of the float mechanism together.

Important! Make sure the lip of the seal fits snugly into the groove in the cap of the float valve.

Repairing the float mechanism

If the float mechanism isn’t working properly, it may need adjustment, descaling or changing.

Adjusting the float mechanism

Empty the cistern.

  1. Close the water supply valve.
  2. Flush the toilet

The cistern overflow must always be above the maximum water level. Water running into the toilet bowl may indicate that the float is set too high. Proceed as follows to lower the float and the water level:

In the case of a knob type flushing control:

  • The float valve (also known as a ball-cock) is operated by a float (or ball) filled with air, fixed to the end of a rod. Bend this rod gently down to lower the float at the end.

In the case of a single-button flushing control:

  • Locate the adjuster screw on the rack and unscrew it to lower the float.

In the case of a double-button flushing control:

  • Adjust the part flush by means of the small pivoting float. The part flush water level should be 25mm below full flush level.
  • Adjust the part flush by means of the small pivoting float. The part flush water level should be 25mm below full flush level.
  • If the problem persists, the float mechanism may be fouled with limescale.
Descaling the float mechanism

Empty the cistern.

  1. Close the water supply valve.
  2. Flush the toilet.

Unscrew the float mechanism from the water supply valve outside the cistern using adjustable pliers. Remove the float mechanism from inside the cistern and open it.

Soak the parts for one hour (or longer if necessary) in white vinegar, then rinse. Wipe off any remaining limescale with a cloth. Assemble the various parts of the float mechanism. Fit the float mechanism to the cistern and reconnect it to the water supply

Turn the water supply on and test the mechanism.

If the problem is solved, put the cistern cover back on. If the fault persists, you’ll have to change the float mechanism.

Changing the float mechanism

Empty the cistern:

  1. Close the water supply valve.
  2. Flush the toilet.

Unscrew the float mechanism from the water supply valve outside the cistern using adjustable pliers. Remove the float mechanism. Fit the new float mechanism to the cistern and connect it to the water supply. Turn the water supply on and test the mechanism.

Adjust the water level to determine the quantity of water released in each flush:

  • Lower the float to lower the water level.
  • Raise the float to raise the water level.
Repairing the flush mechanism

Empty the cistern:

  1. Close the water supply valve.
  2. Flush the toilet.

Remove the flushing mechanism from the cistern by turning it 1/4 turn anti-clockwise. Once free, lift the mechanism vertically out of the cistern.

Remove the plug seal and the flushing valve seal from the mechanism and wipe them clean with a cloth. Check them for wear. If they are worn, fit new ones. Soak the mechanism and its seals in white vinegar for a good hour (or longer if necessary). Clean the bottom of the cistern with a sponge.

Fit the descaled seals to the flushing mechanism: first the plug seal then the flushing valve and its seal.

Frequently Asked Questions

What are the three common faults in a cistern toilet?

The three common faults are a leaking or faulty flush valve or flapper, a worn or misadjusted fill valve, and problems with the handle or lift chain. A faulty flapper or seal lets water run into the bowl, a failing fill valve causes slow refill or continuous flow, and a broken or loose chain or handle prevents a full flush. Mineral build-up and worn seals are frequent causes.

How to fix flush on toilet cistern?

Start by isolating the water supply and removing the cistern lid, then check the chain or push-rod for correct length and connection. Inspect the flapper or flush valve for wear and replace if it won’t seal, adjust the float or ballcock to correct water level, and clean or replace the inlet valve if filling is slow. Reattach the lid and test the flush, seeking a replacement cistern kit if parts are damaged.

How to fix a toilet cistern that is running after flushing?

If your cistern runs after flushing, it usually means the inlet valve or flush seal is not closing properly. Turn off the water, lift the cistern lid and check the flapper or seal for wear or debris, clean or replace it if needed, and inspect the float or fill valve for correct height and movement, adjusting or replacing the valve washer as required. Also check the valve seat for limescale and tightness of connections. If you are unsure, contact a qualified plumber.

Can you replace the flushing mechanism in a toilet?

Yes, you can replace a toilet’s flushing mechanism. Most cisterns allow the internal flush valve, fill valve or complete flushing kit to be swapped while the cistern is isolated and drained. Choose a replacement compatible with your cistern type or a universal kit, follow the manufacturer’s fitting instructions and turn off the water supply before starting. If you are unsure about compatibility or plumbing skills, consider getting help from a qualified plumber.