Why Drains Keep Blocking in Greenwich

A drain that blocks once is an incident. A drain that blocks every few weeks is a condition, and conditions have causes. In Greenwich the causes are well understood and fall into a small number of groups, which is useful, because each one has a different answer. This guide sets out what those causes are, which parts of the borough each one shows up in, and the point at which another clear-out stops being worth paying for.

Four Different Causes, Four Different Answers

The first is ordinary domestic loading: fat, soap and hair scale in the pipe wall and narrow the bore until the run cannot carry a normal flow. The second is roots, which do not bore through sound pipe but find open joints and cracks where there is water and air to encourage them. The third is a physical defect: a collapsed length, a step where the pipe has dropped, or a crack that lets the surrounding ground wash in. The fourth is capacity, where the run and the gully and the public system are all asked to do more at the same moment.

Symptoms overlap, which is why guessing does not work. A slow drain that never fully recovers looks the same whether the cause is scale or a collapsed section, and a kitchen sink that backs up and then clears looks the same whether the blockage is downstream or the pipe is simply too narrow. This is the argument for looking rather than repeating.

The Three Build Phases Under Charlton And Blackheath

The Rectory Field appraisal in Charlton gives an unusually clear picture of how this happens. Almost all the buildings are small Victorian terraced houses of yellow or mixed London stock under slate roofs, built in three phases: early Victorian before 1867, mid-Victorian after 1867, and late Victorian by the end of the 19th century. A street of terraces laid in three phases has three sets of house drains, and the later ones were connected into the earlier ones because that was the only route available.

Those junctions are where failures begin. A connection cut into a barrel that was never designed to take it is a weak point, and ground movement over many years opens it. The borough's conservation areas include West Greenwich, designated 1968, East Greenwich, designated 1992, and Blackheath, and the Rectory Field appraisal records that most houses there are covered by an Article 4 Direction. None of that affects the pipe, but it does mean that where a permanent repair is eventually needed, it has to be planned around the frontage.

Why The Public Sewer Here Is Different

Greenwich sits over a network built for a different city. South of the river, London's low-level sewer runs to Deptford for pumping, and the Bermondsey branch joins it at High Street, Deptford. Greenwich Pumping Station, called Deptford Pumping Station until about 1986, was built in 1864-65 in London stock brick in the Italianate style as part of Bazalgette's scheme, lifting sewage 18 feet into the Southern Outfall Sewer. It is operated by Thames Water and the site is Grade II listed, and it also carries a shaft for the Thames Tideway Greenwich connection tunnel, 4.5 km long, which links into the 25 km Tideway Tunnel.

A pumping arrangement means the network does not simply flow downhill to a downstream point; it has to be lifted. That makes it more sensitive to solids arriving in a surge than a gravity sewer would be. Thames Water is also opening more than twenty new pumping stations across London, so the system is being reworked while the old stock is still carrying the load. If a blockage turns out to be on the public side, it is Thames Water's responsibility, not the household's, and the distinction is established by finding the last access point before the boundary.

London Clay, The River And The Twelve Critical Drainage Areas

The borough's surface water strategy records that a large part of Greenwich away from the Thames overlies London Clay, while land adjoining the Thames and other river corridors overlies Alluvium and River Terrace deposits. Clay does not absorb rainfall. Every downpour has to be carried by the drains, and the same strategy records that the Drain London project identified 12 Critical Drainage Areas in the borough, including one at Cutty Sark, which is where the surface water system was already over capacity.

This is the reason so many households here describe a pattern rather than a series of events: the drain is fine most of the year and fails every time it rains hard for a couple of hours. A partially scaled run has very little spare capacity, so a small extra flow is enough. That pattern is a capacity problem on top of a maintenance problem, and cleaning only ever addresses the second one.

What Jetting Fixes, And What It Does Not

Jetting fixes maintenance. A high velocity water jet breaks up scale, compacted silt and root ingress, and the solids are then removed rather than pushed further along the pipe. That difference is the whole reason a proper clean lasts. What jetting does not do is repair a collapsed length, rebuild a joint that roots have already destroyed, or add capacity to a gully or a public system that is already at its limit.

Our drain jetting in Greenwich page covers the equipment and the process in detail. When a drain keeps failing, the pairing is usually jetting first to clear the line, then a survey to establish what is actually behind the blockage.

What To Do Before You Enquire, And What To Ask For

Before you enquire, note where it backs up and how long it takes to clear on its own. A gully that clears slowly points at the run; a gully that stays full points at something further along. Note the date and the weather, because a pattern that only appears in heavy rain is a different problem from one that appears after a fortnight of no rain. And if a previous engineer has already been out, ask what they found rather than what they did, because the two answers are often different.

When you do call, ask three things: whether the price is fixed before the work starts, whether there is a callout fee, and whether a survey would change what needs doing. The first two are straightforward. The third is the one that separates a clear-out from a diagnosis. For the wider picture, our drain unblocking in Greenwich page covers response and coverage across the borough.

Last Updated: 23 September 2026