How to Fix A Constantly Running Dual Flush Toilet

Last Updated on January 5, 2022 by toilethaven

Why is My Dual Flush Toilet Constantly Running?

If you have a dual flush toilet that is constantly running, most likely the dual flush valve seal is worn out, warped or dirty and hence not sealing properly. It could also be as a result of a defective fill valve continuously filling the tank.

If the toilet fill valve is the problem, it will keep on filling the tank with water which will flow down to the toilet bowl through the overflow tube. This is could be one of the reasons why your toilet won’t stop running.

A toilet fill valve is toilet tank part installed mostly on the left-hand of the tank. It is connected from underneath the toilet tank to the water supply line and its function is to fill the toilet tank after every flush.

In dual flush toilets, a float cup/cylinder is connected alongside the vertical body of the fill valve.The float controls the opening and closing of the fill valve and also the water level in the toilet tank.

toilet fill valve

When you flush the toilet, the float moves to the bottom of the tank and the fill valve which until that moment was shut opens and starts filling the tank.As the tank fills with water, the float moves up gradually up to its set height where it will stop and the fill valve will shut. The water level in the toilet tank should be about ½ inch below the overflow tube.

If the height of the toilet float is set higher than recommended, the fill valve will continuously be filling the tank with water as the excess water runs down to the bowl through the overflow tube.

Apart from the toilet float, the fill valve could also be defective in a such away its not shutting even after the tank is full and the float gone up to its position. It will therefore continuously fill the tank with water and will need to be replaced.

The overflow tube is a large pipe in the middle of the tank that sends excess water back to the bowl to avoid overflowing.

Diagnosing a Constantly Running Dual Flush Toilet

Before proceeding to fix a constantly running toilet, you will need to be sure whether the problem is with the fill valve or the toilet seal. To do this, lift off the toilet tank lid and place it away in safe place where it cannot fall and crack.

Check at the level of the water inside the tank relative to the overflow tube. If the tank is full of water such that it is flowing through the overflow tube then the problem is with your fill valve or toilet float.

A toilet float height can be easily adjusted while a faulty or leaking fill valve will have to be replaced. New toilet fill valves are sold with the toilet float included.

If however the problem does not seem to be the fill valve or float, the problem will most likely be the toilet seal.

How to Fix a Dual Flush Toilet that Constantly Runs

To fix a constantly toilet, you may or may not need to replace some toilet parts. If for instance the dual flush valve seal is misaligned or just dirty, you will only need to fix it. If however it has hardened with time or is worn out then you will need to replace it.

How to Fix/Replace a Dual Flush Toilet Seal

Most of the time when you a dual flush toilet that won’t stop running, the problem is normally with the seal. Let us see how to fix or replace a dual flush seal.

  • Turn off the water supply to the toilet. The toilet shut off valve is located on the wall behind the toilet. Turn this valve clockwise.
  • Flush the toilet and hold the flush lever down to remove as much water as possible from the toilet tank.
  • Remove the toilet tank lid and place it away in a safe place.
  • Hold the dual flush valve body firmly and give it a turn clockwise or counterclockwise to remove it.
  • Carefully check if the seal is worn out, misaligned or is covered with debris/dirt.
  • If it looks worn out or has hardened over time then you will need to replace it. It’s made of rubber and hence it is elastic. Pull it out and put in the new one.
  • On the other hand if the seal look dirt, clean it with running water in a sink. Remember to also clean the flush valve opening where the seal sits.
  • if the seal was misaligned, try and straighten it. You should also consider applying Vaseline on it which helps in sealing.
  • Put back the valve as you removed it and align the flush buttons as they were before
  • Turn on water supply to the toilet and let the tank fill.
  • Check and listen carefully for any water trickling into the toilet bowl.
  • Hold a piece of tissue paper against the toilet rim and see if it remains dry.
  • If you are happy with everything put the toilet tank lid back on and flush the toilet a couple of times just to be sure it is working efficiently.

How to Adjust A Dual Flush Toilet Tank Water Level

If you dual flush is running because of excess water in the tank, this is how you fix it:

  • Turn off water flow to the toilet and flush the toilet.
  • Remove the toilet tank lid and place it away.
  • Alongside the toilet float, you will see a long plastic screw. This screw is used to adjust the height of the float cup and consequently the water level in the tank.
  • Use your hand or a screwdriver to turn this screw counterclockwise.
  • Open the water supply to the toilet and notice the new level of water. It should be about 1-1/2 inch below the overflow tube.
  • Adjust the screw until you get the desired height.
  • Flush the toilet a couple of times and see if the water comes back to its set height.
  • Put the toilet tank lid back.

How to Replace a Toilet Fill Valve

If the toilet fill valve is the culprit then you will need to replace it. Some people will try and fix the fill valve but the best thing and the long-term solution is to get a new one. Fill valves cost about 20 dollars and can serve you for more than 5 years. Fluidmaster’s and Korky’s fill valves are among the best.

To replace a toilet fill valve follow this detailed guide here.