A sewer camera inspection is a strong tool and an imperfect one, and the imperfections are mostly in how it is used rather than in the camera. A line can be inspected and reported sound and then collapse a year later, and when that happens the question is whether the defect was there to be seen. Often it was, and the inspection missed it for one of a small number of reasons that recur. Knowing them lets a customer ask the right questions of a report, and lets an operator avoid them on the next job.
Quick answer: inspections miss problems when the pass stops at the first blockage and the pipe beyond is never seen; when the camera moves too fast past joints; when the LEDs are at full power and the defect is lost in glare; when a fixed head rolls and the invert, where most defects are, is not in view; when standing water or sediment hides the bottom of the pipe; when a dry-season pass cannot show infiltration; when branches, the stack or the section under the slab are not entered; and when the operator does not recognise what the picture shows. Each is a question to ask of the report.
The pass stopped early
A camera that reaches a blockage and stops has inspected the pipe up to the blockage. The pipe beyond is unknown, and a report that does not say so leaves the customer assuming it is sound. The remedy is to clear the line and inspect again, or to enter from the other end. The collapse guide describes the stop, and the follow-up guide the second pass.
Too fast
A clay lateral has a joint every few feet and every joint is a possible defect. At walking pace a joint passes in a second, and a hairline gap, a thread of root or a small step is gone before it registers. The remedy is to slow down at joints, which doubles the inspection time and is the difference between looking and inspecting. How long an inspection takes explains why a short inspection is a warning.
Wrong lighting
Twelve LEDs at full power on a wet or pale pipe wall produce glare, and a crack, a scour mark or a gap is lost in it. The remedy is to dim the lights until the wall shows texture, which most operators know and some forget. The adjustable LED guide and LED lighting in dark pipes cover the technique.
A rolling picture
On a fixed head the picture rotates as the rod twists, and the invert, where cast iron channels, where holes form and where bellies hold water, may be at the top of the screen when the camera passes a defect. A self-leveling head keeps the invert at the bottom. An operator with a fixed head has to track the orientation consciously, and many do not. Fixed vs self-leveling heads explains the difference in what is seen.
Water and sediment
A belly full of murky water hides its own invert and the joints in it. A bed of sediment hides the bottom of the pipe for its whole length. A camera cannot see through either, and an inspection of a silted or flooded line is an inspection of the crown and sides. The remedy is to clean first or to state the limit. Can a sewer camera see through water and sediment beds cover what is hidden.
The wrong season
Infiltration shows when the water table is up; in a dry month the leaking joints are dry and the inspection finds nothing. Root growth is heaviest in late summer. Frost damage shows in spring. A single pass in the wrong season misses the seasonal defects, and a report should state the conditions. The infiltration guide and scheduling an inspection cover timing.
Not entered
The lateral was inspected; the building drain under the slab was not. The main run was inspected; the kitchen branch, galvanized and rusting shut, was not. The stack was never looked at. A report that does not say what was not inspected implies it was, and the customer finds out when the branch fails. The under-slab inspection guide shows how many entries a full inspection needs.
Not recognised
The picture showed the defect and the operator did not know what it was. Loose oakum called roots, a flat run called a belly, channeling called scale, a dry joint not seen as a gap. Experience is the remedy, and the guides on this site on each defect are a substitute for some of it. Interpreting sewer camera footage is the starting point.
What a customer can ask
Did the camera reach the main, and if not where did it stop. How long did the pass take. Was the head self-leveling. Were the lights dimmed in pale pipe. Was the line clean enough to see the invert. What season and weather. Which entries were used and which parts of the system were not inspected. And can I see the whole recording. The questions to ask before hiring and the limitations guide cover the rest.
Common questions
Can a sewer inspection miss a collapse?
If the collapse is beyond a blockage the camera could not pass, or in a branch that was not entered, yes.
Why did my inspection say the line was fine?
Ask what was inspected, from where, in what conditions, and look at the recording. The answer is usually one of the eight above.
Is a second inspection worth it?
If the first was short, dry-season, single-entry or by a fixed head, often yes.
Related guides
See what a professional inspection includes, red flags in a report, and what a sewer camera cannot detect.