How to replace a toilet flush valve seal

Toilet paper test

To make sure that you really do have a leak on your hands, start by carrying out the toilet paper test. This test involves taking a piece of toilet paper and placing it in the base of the toilet bowl just above the water line.

• If the toilet paper gets wet that means that there is water dripping from the cistern which indicates a leak.

• If the toilet paper doesn't get wet, there is no leak and there's no need to replace the seal.

This test is important since it can be difficult to spot a tiny leak by sight alone. Performing the toilet paper test will remove any doubts.

Toilet refilling by itself

Another sign that can point towards a flush leak is if your toilet cistern is filling up on its own. If you hear the fill valve starting to go off by itself without anyone flushing the toilet, this means that the cistern is emptying by itself either through the flush seal or through another part of the flush system. The fill valve is simply being triggered to make up for the leak.

Steps

• Shut off the water and isolate the toilet fill valve

• Access the toilet cistern

• Replace the flush valve seal

• Reassemble the toilet cistern

• Reconnect the water inlet and turn on the water

To perform this type of task, it is not necessary to turn off the water at the mains.

• Simply isolate the water supply to the cistern then flush the toilet to empty it.

• Unscrew the nut that links the water inlet to the cistern. Be careful at this point if your pipes have plastic threads as they tend to break quite easily.

• Disconnect the supply pipe from the cistern once the nut is loosened.

A toilet is made up of two main parts: the toilet bowl and the cistern.

• Unscrew the flush control.

• Remove the cover from the cistern.

• Unscrew the cistern. To do so, look for the two screws with wing nuts that are holding the cistern to the toilet bowl. Unscrew the wing nuts by hand to release the cistern. If the screw threads have rusted, use a bit of penetrating oil and water pump pliers to get the wing nuts moving. On some modern toilets, the wing nuts are made of plastic to prevent this type of corrosion. The screws may be made of metal or plastic.

• Once the screws are loosened, remove the cistern and pour any remaining water down the toilet. Set the cistern on a towel on top of the toilet seat. There may be sediment at the bottom of the cistern. If so, be sure to clean it.

• Remove the doughnut washer that sits between the cistern and the toilet bowl.

• Clean it with a sponge and wipe down the surrounding area with a cloth. The surface should be clean and the washer should be in good condition. Replace if necessary.

• Disassemble the toilet flush valve either by unscrewing the nut holding it to the cistern or rotating it a quarter turn to the left, depending on the type of flush valve you have.

• Remove the flush valve and use a sponge to clean the area where the seal sits on the inside. This surface must be clean.

• Replace the worn flush valve seal at the base of the valve with an identical new seal.

• Reassemble the flush valve by either securing the nut that holds it to the cistern or by screwing it back into place by turning it a quarter turn towards the right (depending on the model).

• Reposition the doughnut washer between the cistern and the toilet bowl. If you notice that there is any limescale build-up in the flush valves, clean using white vinegar or leave to soak for a few hours in a 30% vinegar-water solution. If there is sediment in the toilet cistern, it is possible that there is some in the valves too. Be thorough and clean everything carefully.

If the screws are rusty, replace them with a new set of fixings. Insert the screws into their holes.

• Position the cistern on the toilet bowl making sure that the seal is in the correct position.

• Tighten the wing nuts onto the screws making sure that the cistern is positioned correctly.

Once the cistern is back in place, you will need to reconnect the fill valve to the water supply. To prevent any unexpected surprises, it's always a good idea to replace the washer that sits between the nut and the plastic threaded joint.

• Put a new rubber washer in place.

• Line the fill valve up with the water inlet.

• Screw the two parts together by hand.

• Finish tightening using a spanner but take care not to overtighten.

• Turn the water supply back on and proceed to filling the tank.

• Check for any sign of leaks and/or carry out the toilet paper test again. If the paper is dry, then your job is done. If it is wet then you can try to tighten up the wing nuts a bit. If the leak persists then this generally means that your flush valve needs to be replaced.

Required skills

Replacing a flush valve seal doesn't require any particular skill so long as you follow all the steps set out in this guide.

Time required

30 minutes to an hour

Number of people required

1 person

Tools and equipment

• Adjustable pliers

• Adjustable spanner

• Cloths

• Penetrating oil

• Cistern fixings

• Flush seal

Safety and workwear

• Gloves

Please note: this is a non-exhaustive list; be sure to match your personal protective equipment to the job at hand.