Signs to look for
- Water rising in the pan after flushing instead of draining
- Water draining very slowly, or gurgling
- Other sinks, baths or showers draining slowly at the same time
- Water backing up from a drain cover or gully outside
What to do first
Stop flushing
Each flush adds a cistern of water. If the cistern is refilling, you can close the isolating valve on the pipe feeding it with a quarter turn of a flat screwdriver.
Check other drains
Run a little water in the nearest basin and bath. Ask neighbours if they have problems. Upstairs affected but downstairs fine usually points to a blockage inside the home.
Try a toilet plunger
Use a plunger designed for toilets, with gloves on. Push gently first to push out air, then use firm pumps. Protect the floor with old towels.
Do not mix chemicals
Avoid pouring drain chemicals into a blocked pan. They can splash, react with other cleaners and make it unsafe for whoever clears it.
Wear gloves and wash hands well. Keep children and pets away. If sewage is coming up through an outside drain or into a downstairs room, avoid contact and get help.
Possible causes
These are common causes, not a diagnosis. The actual fault is confirmed on site.
Things that should not be flushed
Thames Water asks people to flush only the three Ps: pee, poo and paper. Wipes, including those labelled “flushable”, period products, nappies, cotton wool and floss all cause blockages.
Too much paper at once
Usually clears with a plunger.
An object in the trap
Toys, toothbrushes and air fresheners can lodge in the bend of the pan and need careful removal.
Drain blockage further down
If several fittings or an outside drain are affected, the blockage is likely in the drain rather than the toilet.
How WHP would assess it
- Establish whether it is the toilet, the branch pipe or the main drain.
- Clear the blockage using a suitable method for where it is.
- Check that the toilet and nearby fittings drain properly afterwards.
- Tell you if something points to a recurring problem in the drain, or to a section your water company is responsible for.
We explain any call-out or diagnostic charge before booking, and agree the repair and its cost with you before carrying it out.
What affects the price
Every repair is different, so we do not publish fixed prices for this work. These are the things that make the most difference:
- Where the blockage is: the pan, the pipe from it or the drain outside
- What is causing it, for example an object stuck in the trap
- Access to the drain and any inspection chambers
- Whether the toilet needs to be removed to retrieve an object
Before you call
Useful to send us
- Your postcode and whether it is your only toilet
- Whether other sinks, showers or outside drains are affected
- Whether neighbours have the same problem
- Anything you know was dropped or flushed
Get professional help when
- A plunger has not worked, or the pan is close to overflowing
- It is the only toilet in the property
- More than one fitting is backing up
- Something solid has been flushed
Common questions
Is a blocked toilet my responsibility or the water company’s?
Thames Water says pipes and fittings inside your home, and drains within your boundary that serve only your property, are yours. Shared drains and public sewers are the water company’s. If neighbours are affected too, or the problem is outside your boundary, report it to your wastewater company.
Can I use caustic drain cleaner?
It is best avoided on a blocked toilet. It rarely shifts a solid blockage, and the standing water then becomes hazardous for anyone clearing it.
Are “flushable” wipes OK?
Thames Water says no. Wipes go in the bin, even if the packet says flushable.
Sources
Safety and responsibility details checked against these sources on 12 October 2026. Water supplier guidance can change. Check your own supplier’s current advice.