A toilet that blocks once is bad luck. A toilet that blocks every few weeks has a reason, and clearing it again without finding that reason just books you the same job next month.

There is a real difference between a blockage and a recurring blockage, and they get investigated differently.

What a plumber actually checks, and in what order

1. What is actually going down it?

Wet wipes are the single biggest cause of recurring blockages we attend, including the ones labelled flushable. They do not break down like paper does and they catch on anything slightly rough inside the pipe.

Sanitary products, cotton buds, kitchen roll and dental floss all do the same. If the household has changed, a new lodger or children starting to use the bathroom unsupervised, that often lines up exactly with when the blocking started.

2. Is the flush volume enough for the run?

Modern short-flush toilets use considerably less water than the ones they replaced. If a low-flush toilet has been fitted onto an older drain run that was designed around a larger flush, there may not be enough water to carry waste along the pipe.

It gets left partway along, builds up, and blocks. This is a genuinely common problem in properties where the bathroom has been modernised but the drainage has not.

3. Is there a partial blockage further down?

If plunging clears it for a fortnight and then it returns, the obstruction is probably not at the pan. Something downstream is catching material each time.

Lifting the inspection chamber cover while someone flushes tells you immediately whether the water is running away freely or backing up.

4. Is the pan connector damaged or badly fitted?

A connector that is cracked, partly pulled out, or pushed too far into the branch creates a lip inside the pipe. Every flush catches on it. It is invisible from outside and it is a recurring blockage generator.

5. Does the drain run have enough fall, or too much?

Too little fall and solids do not move. Too much and the water outruns the solids and leaves them behind. Both cause repeat blockages and both are usually the legacy of an extension or a bathroom moved to a new position.

This is where a camera survey pays for itself, because it shows the fall and the condition of the run rather than leaving it to guesswork.

6. Is the drain bellied, cracked or root damaged?

A dip in the pipe holds water and catches everything passing through. Tree roots find cracked joints and grow into the pipe, forming a mesh that traps solids.

Both give exactly the pattern of a drain that clears then blocks again a few weeks later, and both are visible on a camera survey.

7. Is the drain shared?

On many terraced and semi-detached properties the drain is shared with neighbours. If the blockage is downstream of where the runs join, it is a shared responsibility and quite possibly the water authority’s.

What it usually turns out to be

If it is wipes, changing what goes down the toilet solves it permanently and costs nothing. If it is not wipes, and it is genuinely recurring, the honest answer is that it needs a camera down it. Repeat rodding is a way of paying for the same job over and over without ever finding out what is wrong.

When to stop and call someone

Frequently asked questions

Are flushable wipes really a problem?

Yes. They pass the toilet but they do not disperse in the drain the way paper does. They are the most common cause of the repeat blockages we attend.

Why does it block again after being cleared?

Because clearing removes the material, not the cause. If something downstream is catching waste, the next few weeks of use rebuilds the blockage.

Who is responsible for a shared drain?

Generally the water authority once the run has joined with another property, but it depends on the layout. A survey establishes where the blockage actually is, which settles who pays.

Will chemical drain cleaner fix it?

Not on a recurring blockage, and it is unpleasant for whoever has to work on the pipe afterwards.

Need a plumber in Herts, Beds or Cambs?

Vantage Plumbing and Heating covers Hertfordshire, Bedfordshire and Cambridgeshire. The line is answered by a person at any hour of any day, and you get a price before anyone starts. Call 01462 506374 or request a callback.

Related: blocked toilets · CCTV drain surveys · drain blockage · drain repairs.