Common causes of blocked drains in London

Grease and cooking fat can stick to the inside of waste pipes. Food scraps, coffee grounds and other solids add to the restriction. Hot water may move a little of the residue but does not remove the cause, and repeated pouring of fat creates a bigger problem farther along the pipe.

Use a container for cooking fat and put food waste in the bin rather than down the sink. Scrape plates before washing them. A sink that drains slowly, gurgles or leaves water around the plug is telling you to act before the pipe stops altogether.

Hair combines with soap and other residue around a plughole or trap. Removing visible material from a strainer can help, but do not push objects deeper into the pipe. A slow shower, bath or basin may need the trap or downstream pipe cleaned properly.

Toilets are designed for human waste and toilet paper. Wipes, sanitary products, nappies, paper towels and other objects can catch in the pipe even when the packet says they can be flushed. Keep a bin in the bathroom and do not flush anything that does not break down as toilet paper does.

If a toilet is close to overflowing, do not flush it again. Close its isolation valve if you can identify it without forcing anything, keep people away from contaminated water and call a plumber.

A blockage outside may be caused by silt, leaves, debris or roots entering a damaged joint. Heavy rain can expose a drainage problem that was already developing. If an outside gully is full, clear only loose surface debris you can reach safely. Do not lift a heavy cover or enter a drain.

The location matters. One blocked sink may be local to that fixture. Water backing up in more than one place, or returning into a bath or shower, suggests the obstruction may be farther downstream. Tell the plumber which fixtures are affected and whether neighbours have the same problem.

In a flat or terrace, more than one property may rely on the same section of drainage. Do not assume that the nearest visible cover is the source of the problem. Note where water first appears and whether it rises when another fixture is used. A plumber can then consider the accessible pipework, shared sections and the safest way to clear the obstruction without causing further damage.

Stop using the affected fixtures and protect the area from dirty water. Do not mix chemical drain products, and do not use them before a professional visit without saying so. Chemicals can make a later repair unsafe. Keep children and pets away from standing wastewater and ventilate the area without putting yourself at risk.

A plunger may help with a small local obstruction when used as directed, but force is not a substitute for diagnosis. If plunging changes nothing, the blockage is recurring, or water is backing up, stop. Rods or mechanical equipment may be needed, and the correct method depends on the pipe and where the restriction is.

Prevention is mostly about what enters the system. Use strainers, dispose of fats separately, keep wipes and sanitary products out of the toilet, and remove hair from bathroom strainers. Outside, keep gullies clear of leaves without opening anything unsafe. If a blockage returns after clearance, ask for the underlying cause to be checked instead of repeating the same temporary fix.

Record which fixture backs up first and whether the problem follows rain or particular use. This information helps distinguish a local trap problem from a shared or outside drain issue. Hem handles drain unblocking as part of its plumbing service across all London boroughs, inside the M25 and just outside it.

Do not feel obliged to diagnose the pipe before asking for help. A useful description is often enough: say whether the water is slow or standing, which fixtures are affected, whether dirty water has returned, and whether the issue started after rain. That gives the plumber a safer starting point than a guessed cause or a mixture of drain chemicals.