Overflow Pipe Leaking? What It Means and How to Fix It

Contents:

• Key Takeaways
• What Is An Overflow Pipe
• Is A Leaking Overflow Pipe Dangerous
• How To Fix A Leaking Overflow Pipe - Step By Step Guide
• Common Causes Of A Leaking Overflow Pipe By Location
• When To Call A Professional Plumber
• How Much Does It Cost To Fix A Leaking Overflow Pipe?
• FAQs

If your overflow pipe is leaking or dripping outside your house, you’re not alone. This is a common plumbing problem that many homeowners experience.

 

Though it is common, it is still serious and needs to be addressed immediately to avoid potential damage and to prevent water waste.

 

This guide will cover common causes of overflow pipes leaking and what you can do to fix them.

If you’re struggling to understand why your overflow pipe is dripping and what to do about it, this useful guide will help you. There are some important factors to remember:

 

• Simple DIY Fix – Fortunately, a leaking overflow is a symptom of a failed valve rather than an issue with the pipe itself, so can often be fixed with simple DIY.

• Urgency – While not immediately dangerous, if your overflow pipe is leaking outside your house, it must be addressed as soon as possible to avoid potential water damage.

• Fixing Your Overflow Pipe – First locate the source of the issue, isolate the water supply and inspect the valve to determine the cause. After that, it’s usually a simple case of replacing a washer or adjusting a valve.

• When to Call a Professional – If the issue with your overflow pipe is due to a fault with your boiler or expansion vessel, it is always best to consult a professional.

 

Top Tip: Identify the location first. A roofline leak signals a loft tank issue, while ground-level drips usually point to the toilet cistern.

Overflow pipes provide a safe outlet for excess water in your plumbing system. They offer a route for excess water to go through if a tank or cistern fails to shut off, protecting your home from potential flooding or damage.

 

They are effectively your house’s first line of defence against water damage. They are often connected to sinks, toilets, and baths. 

 

They appear outside as a small copper or plastic tube leading out through the wall by the bathroom. Some overflow pipes also emerge from the wall higher than the roofline.

 

There can be different kinds of overflow pipes, depending on where in the home they are connected. The most common components in a home that require an overflow pipe are toilet cisterns, boiler systems, and cold water tanks.

 

An overflow pipe leaking outside the house is not an immediate emergency. However, it is a sign that a mechanism designed for safety is failing and so still requires urgent attention.

Is a leaking overflow pipe dangerous, then? While it may not be as serious as a burst main, a leaking overflow pipe can bear some notable risks:

 

• Structural damage – A dripping overflow pipe could cause water-damaged walls, warped ceilings, and ruined insulation. Any resulting mould growth could also weaken any wooden foundations.

• Internal flooding – If the overflow pipe is leaking and therefore not working properly, there is a risk of internal flooding in the plumbing system.

• Environmental impact – If left unfixed, the fault will allow water to continue to be wasted.

• Financial danger – This can range from increased utility bills all the way to property damage repairs.

Most instances of overflow pipe leaking can be resolved with simple adjustments and DIY-friendly methods. Here is a step-by-step guide on how to fix an overflow pipe.

 

Step 1: Identify the Source

 

To resolve any issues with your overflow pipe, you must first determine why your overflow pipe is dripping. This can be for many reasons, so it’s important to identify the source.

 

If it is an overflow pipe on the ground or first floor, it is likely an issue with the toilet cistern. If it is a pipe nearer to the roofline, the issue will be with your cold water storage tank or central heating expansion tank in the loft.

 

Remove the cistern lid and check the water level. If it is very high, this will be the reason for the leak.

 

Step 2: Isolate the Water

 

Toilet cistern: If it's your toilet overflow pipe leaking, then look for a small isolation valve on the pipe leading into the toilet cistern. Turn this 90 degrees with a screwdriver. If you can’t find an isolation valve, turn off the main water supply for the house.

 

Loft: When the issue stems from your loft, you’ll want to turn off the water supply before making any inspections.

 

Lower water level: Once you’ve done this, you’ll need to try to lower the water level somewhat before inspecting. To do this, flush the toilet, or, if the hot tank is the problem, run a hot tap. This will empty the tank slightly, lowering the water level below the opening of the overflow.

 

Step 3: Inspect the Valve

 

When it comes to inspecting the cause of your overflow pipe’s dripping, there are a few things to look out for:

 

• Obstructions – The issue could be caused by the float being stuck on the side of the tank. 

• Waterlogging – If the float is a classic ball-on-rod, ensure there is no water inside the ball, or else it will need replacing.

• Washer – Within the valve, a faulty rubber washer could be responsible. Its job is to close the water inlet, so if it is not working, it won’t seal and needs replacing.

 

Once you’ve identified the cause, you can begin the repair.

 

Step 4: Adjust or Replace

 

Next, it’s important to determine whether your issue can be resolved with an adjustment or requires replacement.

 

• Adjust – On a plastic or modern valve, lower the float position by turning the screw on top of the fill valve. If it is a brass valve, bend the arm down so the ball sits lower, making the valve close sooner. 

• Replace – If the washer is the issue, take apart the valve head and replace it. If it is the valve itself that is damaged, the entire float valve mechanism should be replaced.

 

Step 5: Test the System

 

Once you’ve made the necessary adjustments or replacements, turn the water supply back on or turn the isolation valve back on.

 

Watch the tank fill, and keep an eye on whether the water shuts off before it reaches the overflow pipe or not. Try this a few times to be sure.

 

Make sure any fittings and areas you worked on are watertight to ensure no leaks.

Overflow pipe leaks can be caused by numerous issues. To discover the true cause, you’ll have to first determine where the leak is coming from.

 

1. Toilet overflow pipe leaking

 

If your toilet overflow pipe is leaking, the fault will likely lie in the toilet cistern. This kind of overflow is triggered when the tank’s water level rises beyond the safety weir or internal pipe. 

 

• Find the Cause – To check if this is the cause of the leak, lift the lid of the cistern and check the water level. If the level is high and water is flowing into the overflow pipe, then it is definitely the cause. 

• Check the Float Valve – Look for a plastic ball or float in the cistern. If it is resting too high, or is stuck or submerged, it is failing to shut off the water.

• Lift the Float Arm – if, when you lift it, the water stops, then the float is stuck; if it continues, it’s the valve that’s faulty.

 

Luckily, adjustment is often enough, and a costly repair may not be necessary. There are two common fixes for this problem:

 

• Adjust the Float – Bending the arm of the float valve gently (if it's a brass valve) or turning the adjustment screw to lower the float level (if it's a modern valve) is a common fix. 

• Replace the Washer – it's possible the washer inside the filling valve is worn and in need of replacement. If the water still runs when the float is lifted, this may be the fix for you.

 

2. Boiler overflow pipe leaking (pressure relief valve)

 

A combi boiler uses a copper pressure relief valve, or PRV, pipe instead of a simpler plastic gravity overflow. 

 

The boiler causing your overflow pipe to leak could be because the valve itself is damaged, or it could be that water is forced to release as a result of the heating system’s pressure reaching too high. The most common cause, though, is a failed expansion vessel. 

 

A quick check of the boiler’s pressure gauge will tell you if the issue is an over-pressurised system or not. If the gauge reads over 2.5-3 bar, then that is what’s causing the problem.

 

Note: Working on gas appliances requires a Gas Safe-registered professional. Do not attempt to repair this yourself.

 

3. Loft tank overflow pipe leaking (cold water storage)

 

If the issue is an overflow pipe dripping high up near the roofline, then it's most likely your cold water tank in the loft. To check this, go into your loft and look at whether the water level in the cold water tank is above the normal, limescale-marked waterline.

 

This is primarily the result of an incorrectly adjusted float valve and can be fixed by adjusting the valve or replacing the washer – make sure to turn off the water supply first.

Most dripping overflow pipes can be fixed with simple DIY methods, but it’s important to know when to call a professional. If you experience any of the following situations, get in touch with a professional plumber to ensure your home remains safe and compliant with UK water regulations:

 

• Boiler Pressure Issues – Issues with boiler pressure are best dealt with by a trained professional to avoid further problems like boiler failure, flooding, or carbon monoxide leaks. Additionally, in the UK, only Gas Safe-registered professionals can legally work on gas appliances.

• Hot Water Leaks – This can be an indication of a faulty expansion vessel or boiler problem, so a professional plumber should be consulted.

• Inaccessible Tanks – If you are unable to safely access the tank to resolve your overflow pipe issues, it is always best to contact a professional.

• Hidden Leaks – If you cannot identify the source of the leak, a professional may be better placed to find the root of the problem.