Toilet overflowing: what to do right now

Stop the water first

A bowl that is rising after a flush is being fed by the cistern refilling behind it. The quickest way to stop it is to take the lid off the cistern. Push the flush valve or rubber flapper at the bottom back onto its seat so no more water drops into the pan, and lift the float or the arm on the fill valve so the cistern stops refilling.

Then turn off the supply. Most modern toilets have an isolation valve on the pipe running into the cistern, usually a small fitting with a slot you turn a quarter turn with a flat screwdriver. Slot across the pipe means off. If there is no valve, or it will not move, turn off the whole house at the stop tap, which in most London homes is under the kitchen sink. Our guide to finding and labelling water isolation valves shows where else to look.

With the water off, lay towels round the base and keep children and pets out of the room. If water has run towards sockets, an extractor fan or a light fitting below, switch the electrics off at the consumer unit before you go near them.

Overflow from a toilet pan is contaminated water. Wear rubber gloves, keep it off your skin, and clean and disinfect hard floors once the problem is fixed. Soaked carpet and underlay usually need to be lifted and dried or replaced.

Work out which kind of overflow it is

Where the water comes from, and when, tells you where the problem is. Watch what happens rather than flushing again to test it.

If only the toilet is blocked

When the bath and sinks drain normally and only the toilet is affected, the blockage is usually in the pan's own outlet or the first metre of pipe. That is the one you can often clear yourself.

First, bail out some of the water with an old jug into a bucket so the bowl is about half full. Plunging a brim-full pan just pushes dirty water over the rim. Use a proper toilet plunger with a flange that fits into the outlet, push down gently to get a seal, then work it firmly in and out a dozen times. If the level drops with a gurgle, the blockage has moved. Our guide on how to unblock a toilet goes through plungers, hot water and washing-up liquid, and toilet augers step by step.

Do not pour chemical drain cleaner into a pan that is full or nearly full. It sits in the bowl, it will not reach the blockage, and it makes the water dangerous for whoever has to clear it next. Do not push a wire coat hanger into the trap either: it scratches the glaze and rarely shifts anything solid.

If the drain is backing up

A toilet on the ground floor is often the lowest opening on the drain, so when the pipe outside blocks, the water from everything else in the house comes out there. If the toilet rises when someone showers upstairs or the washing machine empties, plunging the toilet will not help, and the more water you use, the more comes back up.

Stop using the taps, showers, washing machine and dishwasher. Then look outside for a manhole or inspection chamber cover, usually a square metal or plastic lid in the garden, path or driveway. Lift it only if it comes up easily. If the chamber is full of water, the blockage is further down, between that chamber and the sewer. If it is empty, the blockage is between your toilet and that chamber.

In England, drains and sewers that serve more than one property, and the pipe that runs beyond your boundary, have mostly been the water company's responsibility since October 2011. If neighbours are affected too, or the blockage is past your boundary, report it to your sewerage company. If it is within your own drain, it is yours to clear. Our page on shared drain and sewer responsibility explains how to tell the difference, and our guide for when sewage is entering the home covers what to do if it is coming indoors.

If the cistern is the problem

Sometimes nothing is blocked at all. The fill valve that refills the cistern should close when the float reaches the set level. If it sticks open, water keeps pouring in. On most toilets it then runs into the pan through an internal overflow, so you see a constant trickle down the back of the bowl. On older toilets it runs out of an overflow pipe through the wall instead, so you notice dripping outside.

A bowl only fills over the rim from the cistern if the pan outlet is also partly blocked, so it is worth checking both. Closing the isolation valve stops the water, and the fill valve then needs adjusting, cleaning or replacing. Our guides for when a toilet keeps refilling and for an overflow pipe dripping cover those repairs.

When to call a plumber

Call a plumber straight away if sewage is coming up into the toilet, shower tray or bath, if water is getting through the floor into the room below, or if the toilet is the only one in the house and it is still blocked after careful plunging. The same applies if the blockage keeps coming back within days or weeks, because that points to a problem in the pipe itself rather than something someone flushed.

In a flat, tell your managing agent or landlord and the neighbours below as soon as you can. Toilets on several floors usually share one soil stack, and a blockage low down can overflow from the lowest flat's toilet.

• Sewage or dirty water appearing without anyone flushing
• Water coming through a ceiling or into another flat
• Several fixtures backing up at once
• A macerator toilet that is overflowing or has stopped
• The same toilet blocking again after being cleared

What an engineer will do

For a blocked pan, the engineer will use a toilet auger or plunger to clear it and, if something solid is lodged in the trap, may need to take the pan off to get it out. If the drain is blocked, they will lift the chambers, find which length is blocked and clear it with drain rods or high-pressure water jetting.

If toilets in the house keep blocking, a camera survey shows whether there is a collapsed section, root ingress, a joint that has dropped or a build-up of scale and fat. Our guide on why drains keep blocking explains what those surveys usually find.

For a cistern fault, the fill valve or float is adjusted or replaced, and the overflow and flush valve are checked so it does not happen again.

Get an overflowing toilet sorted today

Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road. We clear blocked toilets and drains, repair cisterns and deal with the water damage an overflow leaves behind. Call 020 4652 8585 and tell us what you have seen: whether it is only the toilet, whether other fixtures are backing up, and whether the outside chamber is full.

Our call-out charge is £60, and the engineer explains what they have found and what the work involves before starting. You can read more on our toilet unblocking page, and our emergency plumbing page explains how out-of-hours visits work.