# Why do pipes get blocked? What you can do to prevent it

Source: https://cantleyvidanjoraltyapi.com/en/blog/why-pipes-get-blocked/

Published: 2026-10-17

## In short

- In most repeat blockages, the way the pipe was laid matters more than what was put down it.
- On a line with too little fall or a sagging section, water stands and sediment settles where it stands.
- Sharp bends and reductions in diameter are the first places where foreign objects catch.
- Roots entering and collapse in lines outside the building can only be confirmed with a camera.
- Improving daily habits lengthens the time between blockages, even on a faulty line.

Pipes block when a flaw that slows the flow meets material that is ready to build up at that spot. Wet wipes, grease or hair alone are often not enough: a pipe laid at the right fall, with a smooth inner surface, carries most of them all the way to the manhole. If the same drain blocks again every month, the cause should be sought in the pipe itself.

We have gone through each cause one by one and added the check or precaution you can take if you suspect it. You can observe some of them yourself, while others only become clear once a camera is lowered into the line.

## Lines laid with too little fall

In waste water pipes, gravity is what keeps the flow moving, so every horizontal pipe must slope gently downwards in the direction of flow. If during a renovation the pipe is left too flat inside the screed to save space, or one end lifts as it is fixed to the wall, the water slows down. Slow water drops the sand, soap residue and hair it carries, and a thin ridge forms on the bottom of the pipe.

The typical sign of a fall problem is a drain that never blocks completely but always runs slowly. After a shower, water stays in the shower tray for a while and then drains away slowly.

- On any visible pipe sections, check whether there is a clear drop in the direction of flow.
- Slow drainage that starts right after a renovation points to a fall error.
- For a firm diagnosis, a camera has to show where the water stands inside the pipe.

## Pipes that sag and belly

A pipe that was laid at the right fall to begin with can still give way over time. PVC pipes in a suspended ceiling with widely spaced support clips soften as hot water passes through and droop between two clips. In underground lines, the same result comes from the fill beneath the pipe settling.

Some water always remains in the sagging section. This small pool turns into a reservoir where grease and sediment collect, and the blockage forms at almost exactly the same spot every time.

- Where the suspended ceiling can be opened, have the clip spacing and the straightness of the pipe checked.
- Check whether the outlet of hot water appliances connects to a long horizontal PVC run.
- Blockages that always end at the same place suggest a sag at that point.

## Sharp bends, sudden reductions and poor joints

Every point where a drain line changes direction slows the flow a little. Using two gentle bends instead of a single right-angle elbow reduces the chance of a foreign object catching. In renovations, common mistakes include connecting a wide pipe to a narrow fitting or adding two bends one after the other.

Places where different materials meet are also risky. If a PVC drain pipe has been forced onto an old cast iron stack with a gasket instead of a proper transition fitting, a step is left on the inner surface at the joint. Hair and fibres catch on this step, and soap and grease stick to them.

- If a new blockage point appears after a renovation, question the joint fittings.
- The pipe diameter should not narrow in the direction of flow. It should stay the same or widen.
- On long lines with several bends and no cleaning point, adding an access hatch for maintenance helps.

## Old pipes with a roughened inner surface

Cast iron and galvanised pipes, common in older buildings, rust and scale on the inside over the years. A rough surface holds far more material than a smooth plastic pipe. Limescale deposits from hard water also build up layer by layer on these rough spots and narrow the inner diameter of the pipe.

On lines like this, a blockage comes back quickly even after it is cleared, because the surface that material sticks to is still there. Seeing the condition of the pipe also matters when choosing the clearing method, since a badly thinned cast iron pipe may not withstand rough treatment.

- On cast iron stacks, look for rust stains, damp at the base of the wall or brown seepage.
- On the camera footage, the thickness of the scale and any cracks are assessed, and a decision is made between cleaning and renewing the line.

## Roots entering and collapsed lines

If the pipe leaving the building runs under a garden or pavement on its way to the street line, tree roots are a risk. Roots follow moisture and enter through the smallest gap at the joints, grow inside the pipe like a fringe and catch everything that passes, like a strainer. In old clay or concrete pipes, ground settlement, heavy vehicle loads or underground works can crack the pipe and partly collapse it.

The signs of these problems usually show up outside the building rather than inside: the water level in the manhole stays high, one spot in the garden stays constantly wet, or the ground sinks.

- If there is a large tree on or near the line, consider roots first when blockages keep returning.
- On lines cleared by cutting the roots, the joint the roots keep coming back through should be found with a camera and repaired.
- A collapsed section cannot be fixed by flushing. That part has to be renewed.

## Habits and daily precautions

Even a correctly laid line blocks when it is misused, while on a faulty line good habits noticeably lengthen the time between blockages. In apartment buildings the shared stack means one flat's habits affect the flats below, so a short reminder from management to residents is also useful.

- The toilet is for toilet paper only. Wipes, sanitary pads, cloths and cotton buds belong in the bin.
- Collect frying oil in a bottle and wipe pans with paper.
- Coffee grounds and food scraps belong in the rubbish.
- Use a hair-catching strainer in sink and shower drains.
- Rinse periodically with warm tap water instead of boiling water.
- Do not make chemical drain openers a habit, as they wear down PVC pipes and seals.

## Frequently asked questions

### Why does a pipe block in a newly built bathroom?

In new bathrooms, the most common cause of blockage is a laying error or building debris. Pipes left without enough fall, too many bends, and pieces of plaster, cement or silicone that fall into the drain during renovation slow the flow from the first day.

### Do PVC pipes block less than cast iron pipes?

Because its inner surface is smooth, a PVC pipe holds less material. Even so, a PVC line with the wrong fall or a sag can block more often than a well-laid old cast iron line.

### Can the fall of a pipe be corrected afterwards?

Yes, the faulty section can be corrected by laying it again. First the point where the water stands is found with a camera. For exposed pipes or pipes inside a suspended ceiling, the work can be done without breaking anything, while for a section under the screed it may be necessary to open up only that spot.

### How can you tell that a pipe is prone to blocking?

The clearest sign is the same drain slowing down at short intervals and the blockage always forming at the same point. In that case, having a camera check done after the unclogging shows the lasting cause of the problem.

## Let's find the cause of the repeat blockage together

If the same drain keeps blocking, you can reach us on 0212 923 66 85 by phone or WhatsApp message. We clear the line without breaking anything and show you the cause on camera.

Phone: 0212 923 66 85 (tel:+902129236685)  
WhatsApp: https://wa.me/905315687185