Installing and curing a CIPP liner is only half the job. Before we consider a drain relining job finished, the liner needs to demonstrate that it actually does what it was installed to do, hold back water and soil pressure along its full length with no gaps, pinholes or delamination. A pressure test, sometimes called an acceptance test, is how that gets confirmed, rather than simply assumed because the liner looks intact on camera.
Quick answer (BLUF)
A relined pipe’s acceptance test typically involves either a low-pressure air test or a water test, sealed at each end of the newly lined section, with a pass criterion based on how much pressure the section holds over a fixed time (commonly a few minutes). A pass confirms there are no through-wall defects in the liner. A CCTV inspection follows or accompanies the pressure test to visually confirm full adhesion, correct wall thickness and clean junction reinstatement. Together, the two checks are what should sit behind any warranty a relining contractor offers, rather than the warranty being a promise made without evidence.
Why a cured liner still needs testing
A CIPP liner cures from a resin-saturated felt or fibreglass tube into a rigid, jointless pipe-within-a-pipe. Visually, on a post-cure camera pass, a well-installed liner looks continuous and smooth along its full length. But a visual pass doesn’t rule out every failure mode. A pinhole from an air bubble trapped during resin saturation, a thin spot where the liner didn’t fully expand against the host pipe wall at a bend, or incomplete cure at one end near an access point can all be difficult to identify from footage alone, particularly if the defect is small. Pressure testing is a physical, quantitative check that catches exactly this category of fault, ones that look fine on camera but wouldn’t actually hold water or gas under real operating pressure.
This matters more for relining than for a new pipe installation, because a lined pipe has effectively one shot at getting the cure right. Unlike a new PVC pipe join that can be re-made if a fitting fails, a defect in a cured liner generally means re-lining that section rather than a simple repair. Catching a marginal cure at the acceptance-test stage, while the job is still open and the crew is still on site, is far less disruptive than discovering it months later as a slow leak or a re-emerging blockage.
Air testing a relined section
Low-pressure air testing is the more common method for sewer and stormwater relining, since it’s faster to set up and doesn’t require managing a full column of water in a pipe that’s still connected to a live system. The lined section is isolated between two inflatable test plugs, one at each access point, and air is introduced to a specified low pressure, typically in the range used for standard sewer acceptance testing.
The test then monitors pressure decay over a set period. If the pressure holds within the allowed tolerance for that period, the section passes, indicating an airtight liner with no through-wall defects large enough to leak air at test pressure. If pressure drops faster than the tolerance allows, that’s a fail, and it means either a defect in the liner itself or, less commonly, a poor seal at a junction that wasn’t fully sealed during the reinstatement step.
Water testing a relined section
A water test works on the same principle, isolating the section and instead filling it with water to a specified head height, then monitoring for any drop in level over the test period. Water testing is more common for larger-diameter stormwater relining or where local water authority requirements specify it, and it has the advantage of directly demonstrating the liner’s performance under the type of load it will actually experience in service.
Water testing takes longer to set up and requires a water source and a means of disposing of the test water afterward, which is part of why air testing is the default choice for most residential sewer relining jobs where either method would be acceptable.
What a passing result actually confirms
A passing pressure test confirms the liner is structurally sound and watertight or airtight along the tested section, at the pressure and duration specified. It doesn’t, on its own, confirm correct liner thickness, full adhesion to the host pipe, or gradient (fall) along the run, those are separate checks carried out through CCTV review and, where fall is a concern, dedicated gradient testing. See our CCTV drain inspection report explained guide for what the accompanying post-cure camera pass should show alongside a pressure test result.
When pressure testing is and isn’t used
Pressure testing is standard practice on new sewer connections and is increasingly requested by water authorities and on larger commercial relining jobs. For a typical residential sewer reline on the Central Coast, a reputable contractor will pair a post-cure CCTV inspection with either a pressure test or a straightforward visual and dimensional check, depending on the pipe diameter, the water authority’s requirements for that property, and whether the job is a full-length reline or a smaller point repair. Ask your contractor directly which acceptance method they use and ask to see the result, a genuine acceptance test produces a specific pass/fail reading, not just a verbal assurance that “it looked fine.”
What it costs
Pressure testing is typically included as part of a standard drain relining job rather than charged separately, since it’s part of confirming the work meets acceptance standards before the crew leaves site. Where a standalone pressure test is requested on an existing liner, for instance as part of a pre-purchase due diligence check on a property with a previously relined pipe, this is generally bundled with a CCTV inspection at $250–$450.
Frequently asked questions
Is pressure testing required by law for residential drain relining? Requirements vary by water authority and by whether the work connects to or affects a public sewer main. For fully private, on-property relining, a pressure test isn’t always a strict legal requirement, but it’s good practice and something a reputable contractor should be willing to do or explain if they don’t.
What happens if a relined section fails the pressure test? The section is re-inspected to locate the defect, and depending on what’s found, either a localised repair or a full re-line of that section is carried out before re-testing. A failed initial test isn’t unusual on a marginal cure and is exactly why the test happens before the job is signed off, not after.
Does pressure testing damage the new liner? No. Air and water testing use pressures well within the liner’s design tolerance. The test is designed to confirm the liner holds at operating pressure, not to stress it beyond normal conditions.
Can I ask to see the pressure test result for my job? Yes, and you should. A specific reading (test pressure, duration, and pass/fail outcome) should be part of your job documentation alongside the CCTV footage, particularly if the liner carries a long-term warranty.
Is a pressure test the same thing as the CCTV camera check after relining? No, they check different things. The CCTV pass is a visual inspection confirming the liner’s physical appearance, adhesion and junction reinstatement. The pressure test is a physical measurement of whether the liner holds air or water at a specified pressure. A thorough acceptance process uses both.
Ask us about the acceptance testing behind your relining quote →