How to Fix a Leaking Overflow Pipe Re July 26, 2022

How to Fix a Leaking Overflow Pipe

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Even if you’re currently unsure what an overflow pipe is or where it’s located, it doesn’t take a genius to figure out that the last thing you want is a leaky one. Overflow pipes are attached to appliances like water tanks, boilers, and toilets that could potentially end up overfilling, thus leading to quite a wet mess for some unsuspecting homeowners to deal with. As you may have guessed by now, the main purpose of overflow pipes is to remove any excess water and ensure that it finds its way to the drainage system.

To say it simply, an overflow pipe leads from a water storage tank or cistern inside your home to the outside and they’re an integral part of your home’s plumbing system. You can commonly find overflow pipes in:

  • Basins
  • Baths
  • Central heating feed and expansion tank
  • Cold water feed and expansion tank
  • Combination boiler
  • Copper cylinder
  • Sinks
  • Toilet cistern

My Overflow Pipe is Leaking

Now that you know what it is, you’re probably wondering what to do in the case that your overflow pipe is leaking. If you haven’t already, you’re going to want to diagnose the cause of the leak.

The most common problem is generally the float valve, which is located inside toilet cisterns, cold water tanks, and expansion tanks. To properly identify the float valve, look for a plastic armature connected to a ball that moves up and down with the level of the water. Whenever the water tank is in use, the water level will change, and the ball on the float valve will rest on the surface of the water. As the float reaches its predetermined setting, the pump will kick on, thus refilling the water in the tank.

So, as you may guess, if the float valve is malfunctioning on your tank, the cold-water feed won’t operate correctly and switch off. This can cause the water level to continue to rise above the overflow pipe and then low-and-behold, you have yourself a leak!

Aside from the float valve being a leading cause of leaks, another guilty culprit could be related to the washers. Washers typically wear out quickly since they’re continuously in contact with water. In some cases, cheap, low-quality washers are used on appliances, and due to their decreased longevity, they can result in pesky leaks.

I Found the Leak, Now What Do I Do?

Whether you have water leaking from the boiler or overflowing from your toilet, before you fix the leak, you need to make sure it’s properly diagnosed.

Once you figure out the problem with the float valve or a washer, it’s time to replace it. But first, you’re going to need to turn off the water to prevent any of it from flowing into the tank.

The following is a safe approach to the most common issues caused by a faulty washer or malfunctioning float valve.

  • Shut off the water flow through the isolation valve inside the pipe that runs to the tank.
  • Flush the toilet to get rid of any access water.
  • Stop the water, not the water tanks. This is done by blocking the water at the turncock.
  • Drain the remaining water by turning by using the facets that run to your toilet.
  • Ensure that you drained enough water to reach the area in which you need to repair

Toilet Overflow Pipe

The overflow pipe to your toilet extends to outside your house and it can overflow if the water level inside your tank doesn’t stop rising. To go about fixing this issue, you’re going to want to take the following steps:

  • First: Check to see if the float valve can move freely with nothing foreign restricting it.
    • Sometimes the issue can be something as simple as the float valve getting stuck on its own rope or chain, or perhaps tangled in something foreign. This is generally an easy fix and just requires you to free it from whatever it’s stuck on.


  • Second: Regulate the float valve.
    • The height of the float valve may be set too high to successfully shut the system off and prevent the overflow from happening. This will require some sort of adjustment on your behalf whether it be bending the metal bar on it or adjusting it via screws.


  • Third: Check the water pressure.
    • The reason the overflow pipe may be leaking could be due to increased water pressure within the pipe. In this case, locate the isolation valve and shut it off to manage the flow.


  • Fourth: Make any needed replacements to the float valve or washer(s)
    • If you’ve tried the other recommended steps but you still have a leak, then the problem is likely the valve itself or one or more problematic washers. For that, just resort to the steps mentioned earlier to replace the faulty washer(s) or float valve.

Expansion Tank and Coldwater Feed Overflowing Pipe Leak

The cold-water feed and enlargement tank overflow pipes extend through the large water cistern and end up outside your home. The purpose of this tank is to provide water to your sinks and if you’re experiencing an issue here, consider the following: 

  • Perhaps the water inlet in the tank is not turning off
    • Look inside the tank and if you find a constant drip from the water feed, try adjusting the float valve or replacing the valve altogether. This problem could also be related to a washer(s) issue.
  • Pressurized water is being sent back into the outlet pipe:
    • If the pipes, float, and washers appear to be working correctly, then the problem is likely related to the water being pushed back from the outlet pipes, resulting in a leak. This problem will generally require the help of a professional.

Overflowing Pipe Of Central Heating Feed

Just like the cold water feed, the overflow pipe from the central heating feed also extends outside your home. The purpose of this pipe is to feed water to the central heating system of the house. Problems with this type of leak are associated with two main culprits.

  • Issues with a hot cylinder
    • If your cold-water feed is working properly, and the float valve and washer also appear to be undamaged and in good working order, then a probable cause could be because of issues with your hot water cylinder.
  • The water feed doesn’t stop inside the tank
    • If you notice constant water dripping into the tank, make sure that the float valve isn’t broken or damaged. Be sure to also check the washers, as they could have worn down over time. If you come across such issues, follow the above-mentioned procedure of replacing the float valve and washer.

Boiler Overflow Pipe Leaking

Boilers also have a pipe that looks like an overflow pipe, and on it, you’ll find a pressure relief valve. The purpose of this valve is to release water in the case that the system is under too much pressure. Since this valve only flows when there is a problem in the system, you should immediately act if you see it.

A leak in this pipe may be due to excessive pressure on the system or because of problems with the pressure valve. In either situation, it is highly advisable to call a professional service for help.

It’s important to mention that you should take caution not to mistake the pressure valve pipe with a condense pipe as the condense pipe also flows when the central heating system is turned on, and hot water runs through it.

Kitchen Sink Overflow Pipe Leaking

The kitchen sink overflow is located underneath the sink and the purpose of it is to of course prevent your sink from overflowing. Most commonly the biggest culprit leading to this type of overflow is simply a clogged drain. It can easily be dealt with on your own, unless the clog is bad, in that case, a professional service may be required.

Good Luck!

Hopefully, this article helped save you some time and money, as well as cut back on any stress that a leaky overflow pipe could cause.

It’s always important to remember that if you come across an issue with your central heating system or cold-water feed or expansion that you’re unable to repair yourself, it’s highly recommended that you seek help from a professional. Stay safe and good luck!

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