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Blocked Toilet
The pan fills and drains slowly, or does not drain at all, and a second flush makes it worse.
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What's happening?
A toilet blockage sits in one of three places, and where it is determines who clears it. Most are in the pan itself or the first metre of the branch behind it — the classic wad of wipes, excess paper or something that should never have gone down. Some are further along the private drain that serves your property, which shows up as more than one fitting backing up. And some are in the shared or public sewer, which shows up as the toilet backing up at the same time as the neighbours', or as sewage rising in an outside chamber. Look at what else in the house is misbehaving before you reach for anything: if only the toilet is affected, it is local; if the bath, the shower and the ground-floor toilet are all slow, the blockage is downstream and a plunger will not reach it.
What usually causes it?
- Wet wipes, including those sold as flushable, which do not break down like paper
- Sanitary products, cotton buds, dental floss and nappy liners
- Too much paper in one flush, particularly on a low-volume modern cistern
- A toy, air freshener block or cleaning cage that has fallen into the trap
- A build-up of limescale narrowing the pan outlet in a hard-water area
- Fat and grease from the kitchen combining with wipes further along the shared drain
- A blocked or collapsed private drain downstream, so the toilet is only the first thing to show it
Is it dangerous?
Moderate, because of what it contains rather than what it does. Sewage carries bacteria and viruses, so wear gloves, keep children and pets away, and wash thoroughly afterwards. The practical danger is overflow: a blocked toilet that is flushed repeatedly will spill onto the floor and, in an upstairs bathroom, through the ceiling below. Stop flushing after the first failed attempt.
Can I fix it myself?
Often, if the blockage is local. Stop flushing so the pan does not overflow, and wait — the level usually drops on its own as water seeps past. Use a proper toilet plunger with a flange, not a flat sink plunger: seat it in the outlet and work it firmly a dozen times to push and pull rather than just push. A toilet auger will reach further round the trap without scratching the porcelain. Avoid caustic drain chemicals in a pan that is already full; they sit in standing water, do little, and make the job hazardous for whoever comes next.
When should you call a drainage engineer?
Call a drainage engineer if plunging does not clear it, if more than one fitting is slow or backing up, or if the blockage returns within days — a recurring blockage in the same place usually means a defect in the pipe rather than what was flushed. Call the water company instead, at no charge, if sewage is rising from an outside chamber, if neighbours are affected too, or if the problem is in the shared lateral drain beyond your boundary.
What will the drainage engineer actually do?
- Establish where the blockage is by lifting the nearest inspection chambers and reading the water levels
- Clear the obstruction with rods, a drain machine or high-pressure jetting depending on what it is and where
- Run a CCTV camera through the run afterwards to see what caused it and whether the pipe is damaged
- Flush the run through and prove every fitting in the house discharges freely
- Report and record whether the defect sits on private drain or public sewer, so the right party pays
- Advise on descaling, a defective connection or a repair where the pipe itself is the cause
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