How Much Does a Drain Test Cost? Drain Testing in London Explained

What a drain test costs depends on how many runs have to be tested, how easy the chambers are to open, and how many visits the job needs. A single new run between two open chambers on an extension is a short job. Testing several runs, retesting after backfilling, or testing an old drain where the chambers are buried takes longer and costs more. Our labour is priced by time band on the published rate card, and this guide explains what sits behind any drain testing quote in London so you can see what you are paying for before you book.

What is a drain test, and what are you paying for?

A drain test checks whether a length of underground pipe is watertight. You are paying for an engineer's time on site to seal the run, pressurise it with air or water, watch it for a set period and record the result.

The run is closed off at each end with inflatable stoppers, usually from one inspection chamber to the next. An air test pumps the pipe up to a low pressure and checks whether it holds. A water test fills the run to a set level and measures how much water is lost. Either way the answer is a pass or a fail for that run, written down with the readings. The time on site, the number of runs and the paperwork are the three things that make up most of the bill. The equipment itself is standard kit for any drainage engineer, so a quote that adds a large separate charge for "test equipment" is worth questioning.

Which kind of drain test do you need?

Most drain tests in London are booked for one of four reasons, and the reason decides how much testing is needed. Tell whoever is quoting which one applies to you, because it changes the job.

• Building control sign-off. New below-ground drainage, such as the runs for an extension or a new bathroom, is normally tested before the building control body will sign it off. This is often the smallest job: new pipe, open trench, known chambers.
• Before and after backfilling. Building control often wants to see the new run tested again once the trench is filled, because backfill can knock pipes out of line. That is a second visit, and it should be priced as one.
• Checking an existing drain. Buyers, loss adjusters and homeowners worried about damp or subsidence sometimes want to know whether an old drain is leaking. This takes longer, because the chambers may need finding and opening, and old pipes often need cleaning before the test means anything.
• After a repair. A test after a section of drain has been replaced or relined shows the repair holds. It is usually a short job on one run.

What makes a drain test cost more?

Access, the number of runs and what state the drain is in. A clean new pipe with open chambers is quick to test. An old drain with buried chambers, silt and branch connections is not.

• Number of runs. Each length between two chambers is tested on its own. A back addition, a side return and a new utility room can add up to several runs.
• Buried or sealed chambers. Covers that have been paved over, tiled or rusted shut have to be found and lifted before any test can start.
• Gullies and branch connections. Every connection into the run has to be sealed as well, or the test will fail through an open gully rather than a leaking pipe.
• Cleaning first. Silt, scale and debris stop stoppers seating properly and can give a false result. If the run needs jetting before it can be tested, that is a separate item.
• Extra visits. Testing before and after backfilling, or coming back to retest after a fault is fixed, means more than one attendance.
• The paperwork. A short record of the readings for building control costs less than a written report prepared for an insurer or a solicitor.
• Time band. A drain test is almost never urgent, so there is rarely a reason to pay evening or night rates for one.

What happens if the drain fails the test?

A failed test tells you the run is leaking, but not where or why. Finding the fault is a separate job, and fixing it is another, so a fail usually means more than one further line on the bill.

On new work, the first step is to check the test itself. A stopper that has not seated, a trap that has been blown or a temperature change inside the pipe can make a sound run look like a failure, so a marginal fail is worth re-running before anyone digs. If it fails again, a camera is the usual way to find the fault. On a new run the builder normally puts it right and pays for the retest, because a new drain should pass. On an old drain, a fail is common and is not in itself a reason to replace anything. The useful next step is a CCTV drain survey that shows where the joints have opened or the pipe has cracked, so the repair can be priced on what is actually there.

Is a drain test the right thing to pay for?

A drain test is the right answer when someone needs proof that a pipe is watertight, such as a building control officer on new work. It is often the wrong answer on an old drain, because it tells you there is a leak without telling you where it is.

Many older clay drains, particularly those with rigid mortar joints, were never built to hold pressure, so they often fail a test even when they are carrying waste away without trouble. Paying for a test on an old drain can leave you with a fail certificate and no idea what to do next. If the real question is "is my drain damaged, and what would fixing it involve?", a camera survey answers it more directly, and our guide to what a CCTV drain survey costs sets out how that is priced. Some jobs need both: a test to prove there is a leak, then a camera to find it.

Who pays for a drain test on an extension?

On an extension, the test is normally part of the builder's or groundworker's job, because they laid the drain and it is their work that has to pass. Check that it is in their price before you book a separate company.

Where it gets less clear is the old drain the new work connects into. Testing the new pipe on its own is normal. Testing the new pipe together with an old clay run it joins will often fail because of the old run, not the new work. Agree with your builder and building control beforehand exactly which lengths are being tested, and who pays if the existing drain turns out to need work. If an old section under the extension has to be replaced, our drain repair and excavation page explains how that work is priced.

How do you compare drain test quotes?

Compare how many runs each quote covers, how many visits it includes and what paperwork you will receive, not only the total. A quote for one test on one run is not comparable with one that covers every run, a retest after backfilling and a written record.

Ask each company the same questions: which runs will you test, air or water, is cleaning the pipe included if it is needed, what happens and what does it cost if a run fails, is a second visit after backfilling included, and what will I have in writing at the end? Ask whether VAT is included and which time band the work sits in. If you tell us what the test is for and send a sketch or photos of the chambers, we will tell you what the job involves before anyone is booked.