What a blocked drain actually is
A drain is blocked when something narrows the pipe enough to stop water passing. That almost never happens in one moment. A layer of fat lines the pipe wall, silt settles in a low point, a root finds a joint, and the passage closes over weeks or months until one ordinary load of washing is the load that will not go away.
Because the process is gradual, there is nearly always a warning period. A gully that empties more slowly than it used to, a toilet that bubbles when the bath drains, a faint smell outside after rain. Those are the same fault at an earlier and much cheaper stage.
The signs worth acting on
- Water standing in an outside gully long after anything has discharged into it
- Two or more fittings draining slowly at the same time, which points at the shared run rather than any one appliance
- Gurgling from a toilet or plughole when a different appliance empties
- A drain smell outside that gets stronger after rain or in warm weather
- Waste water backing up into a ground-floor shower tray or bath
- Water rising from an inspection chamber
One slow fitting is usually a local problem. Several at once is a drain problem, and it is worth saying so when you call, because it changes what we bring.
How we clear it
We work from the symptom back to the cause rather than clearing the first chamber we open and leaving. Lifting the covers along the run tells us where the flow stops, and that single piece of information decides everything else: which section to jet, at what pressure, and whether the fault is even yours to pay for.
- Open the chambers along the line to find where flow stops
- Establish whether the fault sits inside your boundary or beyond it
- Clear the restriction with high-pressure jetting at a pressure matched to the pipe
- Flush the run and prove the flow from every connected fitting
- Camera the cleared section where the cause is not obvious
Pressure matters more than people expect. The setting that clears a silted gully can finish off a clay drain that has already failed at a joint, so the diagnosis comes first.
Why London property blocks the way it does
Most of the capital’s housing drains through vitrified clay laid in short jointed lengths, much of it Victorian or Edwardian. A century and a half of ground movement has opened many of those joints, and an open joint is both an entry point for roots and a ledge for everything passing by to catch on.
Inner London adds a second factor: combined sewers that carry rainfall and foul waste in the same pipe. During a downpour that network runs full, so a drain already carrying a restriction has no spare capacity at exactly the moment it needs some. It is why so many people first notice a problem during a storm.
The third factor is density. A terraced house converted into four flats still drains through the run built for one household, and a ground-floor restaurant under those flats puts more fat into the pipe in a week than the building saw in a year when it was built.
What it costs
Outside drain clearance is a fixed £144 plus VAT. There is no call-out charge at any hour, on any day of the year, and you get the figure before any work begins rather than an hourly rate that grows while the engineer works.
What the price covers: attendance, diagnosis, clearance and a flow test on every affected fitting. What can change it: if the pipe turns out to be damaged rather than blocked, clearing is not the answer and we will quote separately for the repair once a survey has shown what is actually there. We will say that on the day rather than clear it again next month.
Who pays when the drain is shared
Not every blockage is yours to fund. Since 2011 in England, most shared drains and the lateral running from your boundary to the public sewer belong to the water company, which for nearly all London addresses means Thames Water. A fault on their pipework is theirs to fix, at no cost to you.
Establishing which side of the boundary the fault sits is therefore part of the job, not an extra. We tell you plainly what we found, including on the occasions when the honest answer is that you should call Thames Water rather than pay us.