By Jon Taylor, Founder of Maintain Drains

If your drain has blocked once, it could simply be bad luck.

If we clear it and the same drain blocks again a few weeks or months later, I start asking a different question:

Why is waste getting caught there in the first place?

After working in drainage for around 20 years, one thing I’ve learned is that a recurring blockage is often not the actual problem. It is the symptom of something else happening inside the pipe.

You can keep clearing the blocked drain and getting the water moving again, but if there is a damaged joint, tree root, badly deformed pipe or another restriction underground, sooner or later that blockage is likely to return.

Why does my drain keep blocking?

If the same drain keeps blocking, there is usually something repeatedly restricting the flow or catching waste inside the pipe.

Common causes include a build-up of fat or scale, tree root intrusion, displaced pipe joints, damaged or collapsed pipework, poor pipe gradients, pitch-fibre pipe deformation or an object lodged inside the drain.

If a blockage returns after it has already been properly cleared, I will often recommend a CCTV drain survey rather than simply clearing it again. The aim is to see what is actually happening inside the drain and deal with the cause rather than repeatedly dealing with the result.

If your drain blocks once, clear the blockage. If the same drain keeps blocking, start looking for the reason why.

A blockage and the cause of a blockage are not always the same thing

This is probably the most important point I can make.

When somebody calls us because their toilet won’t flush or an outside drain is overflowing, the immediate priority is obviously to get things moving again.

Depending on the blockage, that may involve drain rodding, high-pressure drain jetting or another method of professional drain unblocking.

But successfully clearing a blockage doesn’t necessarily tell us why it happened.

Imagine a displaced pipe joint underground. Toilet paper catches slightly on the raised edge. More waste catches behind it. Eventually enough material collects for the drain to block completely.

We clear all that material out and the drain starts flowing again.

Problem solved?

Not necessarily.

The displaced joint is still there.

That is why the same drain may be perfectly fine for three months and then suddenly block again in almost exactly the same place.

From our point of view, the interesting part isn’t always what was blocking the drain. It is why that particular part of the drain allowed a blockage to develop.

1. The drain wasn’t completely cleaned

Sometimes the explanation is relatively straightforward.

A drain may have been opened enough to restore the flow, but deposits remain attached to the inside of the pipe.

Fat, grease, soap residue, scale, silt and other material can gradually reduce the internal diameter of a drain. Waste then has less space to move through it and is more likely to collect.

This is one reason high-pressure drain jetting can be more effective than simply breaking through an obstruction. High-pressure water can clean material from the internal surface of the pipe and flush it away rather than just creating a path through the middle.

If you’d like to understand the process in more detail, we’ve also put together a guide explaining how high-pressure drain jetting works.

For a one-off blockage caused by accumulated material, a thorough clean may be all that is needed.

But if we’ve cleaned the drain properly and it keeps happening, I want to look further.

2. Tree roots are entering the drain

Roots are one of the more interesting drainage problems because people sometimes imagine a tree root smashing its way through a perfectly good underground pipe.

What we commonly find is that roots have taken advantage of an existing opening such as a crack, defective joint or displaced section of pipe.

Roots are looking for moisture. Once small roots find their way inside a drain, they can continue to grow.

And a root inside a waste pipe makes a very effective net.

Paper, wipes, grease and other material catches on it. The drain slows down, more waste accumulates and eventually it blocks.

We can carry out specialist tree root removal from drains to restore the flow, but we also need to consider how the roots got into the drain in the first place.

If the entry point remains, the roots may eventually return.

That’s why root removal and a CCTV inspection often go together. In some cases the long-term answer may also involve drain relining or repair to seal the damaged section.

3. A pipe joint has moved

A large number of drainage systems are made up of individual sections of pipe joined together underground.

Over many years the surrounding ground can move and joints can become displaced.

Even a relatively small displacement can create a lip inside the drain.

Waste flowing through a healthy pipe should have a fairly smooth journey. Introduce an edge into that pipe and materials can start catching against it.

One item catches another.

Then another.

Eventually you have another blocked drain.

From above ground it can look like exactly the same problem each time. Once we put a camera through the drain during a CCTV drain survey, the reason can become much easier to identify.

4. The pipe itself is cracked or damaged

A cracked drain does not automatically mean the entire pipe has collapsed.

But damage can change the internal surface of a drain and create places for waste to collect.

It can also allow soil, fine roots and other material to enter the drainage system.

Again, simply clearing what has accumulated inside the drain won’t repair the damaged pipe.

Depending on the condition and position of the fault, options can range from a targeted repair to no-dig drain relining, where a new lining is installed inside the existing pipe.

Where a pipe is badly damaged or collapsed, drain excavation and repair may be the more appropriate solution.

Excavation isn’t always the first answer.

Finding out exactly what has failed is.

5. You may have pitch-fibre drains

This is something we come across in older properties and it deserves particular attention.

Pitch-fibre drainage was widely used during the middle of the twentieth century. As it ages, the pipe can deteriorate and deform.

Instead of remaining perfectly round, sections of the pipe can become squashed, blistered or distorted. The result is less internal space for wastewater to pass through.

You can clear a blockage from it and restore the flow, but you cannot unblock your way out of a pipe that is gradually losing its shape.

If we suspect pitch fibre, a CCTV inspection allows us to assess its condition and decide whether specialist pitch-fibre drain repair, relining or replacement is appropriate.

This is also one of the reasons I think drainage is worth considering when buying an older property. A normal viewing tells you very little about the condition of the pipes buried beneath the house and garden.

6. The drain may have the wrong fall

Most domestic drainage relies on gravity.

The pipe needs enough gradient – or “fall” – for water and waste to travel along it properly.

If part of a drain has sunk, moved or was installed with an inadequate fall, water may slow down or sit in a low section.

Solids can then settle instead of being carried away.

Over time that becomes another blockage.

Clearing it makes everything appear normal again, but the low point remains and the process starts over.

This is one of those situations where the frequency and location of the blockages can give us a useful clue. A combination of CCTV inspection and, where the layout itself needs establishing, drain mapping can help us understand what is happening underground.

7. Something may be permanently lodged in the pipe

We find all sorts of things in drains.

Wipes and sanitary products are obvious examples, but building materials and other foreign objects can also find their way into drainage systems.

Occasionally an object becomes lodged in a position where water can still get past it.

That means the drain doesn’t remain permanently blocked.

Instead, the object catches passing waste until a blockage develops. The surrounding material is cleared, the drain works again, but the original object remains.

Then the whole process repeats.

A CCTV camera is particularly useful in this situation because we can actually see what we’re dealing with rather than guessing from the surface.

How soon is too soon for a drain to block again?

There isn’t a magic number.

A drain blocking twice doesn’t automatically mean you’ve got a collapsed pipe underground.

How the property is being used matters too.

A commercial kitchen putting large amounts of fat and grease into its drainage system has a completely different risk profile to a residential property, for example.

What interests me is a pattern.

If we’re being called back to exactly the same drain, particularly after it has already been properly cleaned, there is usually value in investigating further.

Paying repeatedly to clear the same obstruction doesn’t make much sense if something underneath is continually causing it.

When would I recommend a CCTV drain survey?

Not every blocked drain needs a camera survey.

If we attend a straightforward blockage, clear it completely, test the system and everything behaves normally afterwards, CCTV may add very little.

But my advice changes when the problem keeps returning.

A professional CCTV drain survey allows us to inspect inside the pipe and look for:

Tree root intrusion
Cracks and fractures
Displaced or misaligned joints
Collapsed sections
Pitch-fibre deformation
Heavy deposits and scale
Foreign objects
Restrictions in the pipe
Areas where waste is repeatedly collecting

Crucially, it also lets us identify where the problem is.

Instead of saying “there seems to be something wrong with the drain”, we may be able to establish that a fault is a particular distance from an access chamber and then decide on the most appropriate solution.

That can make any subsequent repairs much more targeted.

Does a drain that keeps blocking always need repairing?

No.

And I think that’s an important distinction.

Sometimes CCTV shows that the pipe is structurally fine and simply needs a thorough high-pressure clean.

Sometimes we find a maintenance issue that can be managed with periodic cleaning.

Sometimes there is a relatively small defect that can be addressed using no-dig relining.

And occasionally we find serious damage or a collapsed section where excavation and drain repair genuinely is the sensible option.

The point of investigating isn’t to find an excuse to repair a drain.

It’s to stop guessing.

Can I stop my drain blocking again myself?

Good habits certainly help prevent avoidable blockages.

Don’t pour fats, oils or cooking grease down kitchen drains.
Avoid flushing wipes and sanitary products.
Keep outside gullies clear of leaves and debris.
Pay attention if toilets, sinks or showers suddenly begin draining more slowly.
Don’t ignore recurring gurgling sounds or unpleasant drain smells.

But there is an important difference between preventing avoidable blockages and trying to compensate for a defective drain.

You can’t change your household habits enough to repair a displaced underground pipe joint.

If the drainage system itself is causing the problem, it needs to be diagnosed.

What does it mean if several drains in the house are blocking?

If one sink is slow, the problem may be relatively local to that fixture or waste pipe.

If toilets, sinks, showers and outside drains are all affected at the same time, the obstruction could be further along the drainage system.

It may also be worth establishing whether the affected pipe is private or part of a shared drainage system, particularly where neighbouring properties are experiencing similar problems.

We’ve written a separate guide explaining how to tell if you have a shared drain and who may be responsible.

Where the blockage is located can affect both the solution and who needs to deal with it.

What are the warning signs of an underlying drain problem?

A recurring blockage is one warning sign, but there are others I would pay attention to:

The same toilet or drain repeatedly blocks.
Several fixtures drain slowly at the same time.
You regularly hear gurgling from toilets or sinks.
Outside drains fill up when water is used inside the house.
There are persistent unpleasant drain smells.
A blockage returns shortly after being professionally cleared.
Wastewater appears in a different drain when a toilet is flushed.
Neighbouring properties experience similar drainage problems.
There are signs of movement, subsidence or unusually wet ground near the drain route.

None of these automatically proves the drain is damaged, but they can justify investigating rather than repeatedly treating the symptoms.

When is a recurring blocked drain an emergency?

A drain that occasionally runs slowly is very different from wastewater or sewage backing up into your property.

If toilets cannot be used, sewage is overflowing from a manhole, wastewater is entering the property or there is an immediate risk of flooding, I would treat that as an urgent drainage problem.

In that situation the first priority is restoring the flow safely. Maintain Drains provides 24-hour emergency drain unblocking and drainage assistance across Dorset and Hampshire.

Once everything is safe and flowing again, we can decide whether the reason for the blockage needs further investigation.

Why does my outside drain keep blocking?

If an outside drain keeps blocking, the cause can range from leaves, silt and grease to a restriction deeper within the underground drainage system.

If the drain serves a kitchen, fat and food waste may be contributing to deposits inside the pipe. If it is surrounded by trees or established shrubs, root intrusion may also be worth considering.

Where simply clearing the gully does not solve the problem for long, we may need to clean the drain properly with high-pressure water or inspect the underground pipework using CCTV.

Why does my toilet keep blocking?

If only one toilet regularly blocks, the cause may be close to the toilet itself.

If the toilet blocks alongside sinks, showers or outside drains, however, the problem may be further down the drainage system.

The important clue is whether the blockage is isolated or whether several parts of the property are affected at the same time.

A drainage engineer can usually establish whether the problem is a straightforward obstruction or whether further investigation is needed.

Can tree roots cause a drain to keep blocking?

Yes. Tree roots can enter damaged or defective drainage pipework and create an obstruction that catches paper, grease and other waste.

Clearing the waste may restore the flow temporarily while leaving the roots themselves in place.

If roots are suspected, the sensible approach is usually to identify the affected section, carry out professional drain root removal and inspect the condition of the pipe to understand how the roots entered.

Should I have a CCTV survey if my drain keeps blocking?

If a drain has blocked once, usually not.

If it has been properly cleared and the same problem repeatedly returns, a CCTV drain survey can be a much better use of money than paying for repeated unblocking without knowing why it is happening.

The survey can show whether the cause is simply accumulated material or whether there is a physical problem such as roots, a damaged joint, deformation or a collapsed pipe.

My advice after 20 years working with drains

If your drain blocks once, get it cleared.

If it keeps blocking, start asking why.

One of the easiest traps to fall into is assuming that because water is flowing again, the underlying problem has disappeared.

Sometimes it has.

Sometimes all we’ve done is reset the clock until the next blockage.

At Maintain Drains, if we’re seeing the same issue return, our aim isn’t simply to keep unblocking it. We want to understand what is happening underground and give you a sensible long-term solution.

That might be nothing more than a proper clean.

It might mean removing tree roots.

It could involve repairing or relining a damaged section of pipe.

But whatever the answer is, finding the cause is normally better than repeatedly treating the symptom.

Drain keeps blocking? Let us find out why

If you’re in Bournemouth, Poole, Christchurch or elsewhere across Dorset and Hampshire and have a drain that keeps blocking, Maintain Drains can help.

We can clear the immediate blockage and, where necessary, use a CCTV drain survey to investigate why the problem keeps returning.

Call Maintain Drains on 01202 300 040 or contact the team to discuss the problem.

Frequently asked questions about recurring blocked drains

Why does my drain keep blocking even after it has been cleared?

If a properly cleared drain repeatedly blocks, there may be an underlying restriction or defect inside the pipe. Possible causes include tree roots, displaced joints, damaged pipework, pitch-fibre deformation, poor gradients or an object that continues to catch waste. A CCTV drain survey can help identify the cause.

How many times should a drain block before I have it inspected?

There is no fixed number. One isolated blockage does not normally justify a full investigation. However, if the same drain repeatedly blocks after being properly cleared, especially over a relatively short period, investigating the underlying cause may be more economical than continuing to pay for repeated clearance.

Will drain jetting stop a blockage coming back?

Drain jetting can remove grease, silt, scale and other deposits from the internal walls of a pipe, so it can greatly reduce recurring blockages caused by build-up. However, jetting cannot permanently repair structural defects such as cracks, displaced joints or deformed pipework.

Can a CCTV survey tell why my drain keeps blocking?

In many cases, yes. CCTV inspection can identify visible causes including root intrusion, damaged or displaced joints, cracks, collapsed sections, pitch-fibre deformation, debris and areas where waste is accumulating.

Do recurring blockages mean my drain has collapsed?

No. A collapsed drain is only one possible cause. Many recurring blockages are caused by less serious issues such as deposits, roots, localised damage or displaced joints. Inspection is the best way to establish the actual cause before deciding whether repair work is needed.

Can tree roots grow back after drain root removal?

They can if the opening that allowed the roots into the pipe remains. Root removal clears the intrusion, but CCTV inspection can also help identify cracks or defective joints that may need repairing or relining to reduce the risk of the roots returning.

Who is responsible if the blocked drain is shared with my neighbour?

Responsibility depends on where the blockage is located and whether the pipe serves only your property or multiple properties. Read our guide to shared drains and drainage responsibility for more information.