Guides · Harrow

What to Do While You Wait for an Engineer

If a drain is backing up, the half hour before an engineer arrives determines how much damage you are left with. The steps below limit that damage and make the job faster when they do arrive. They are deliberately simple - none of them requires tools or any risk to you.

Stop putting water into the system

This is the single most useful thing you can do and the one most people miss. Every litre that goes into a blocked drain has to go somewhere, and if the run is obstructed it comes back up at the lowest point - usually a ground-floor toilet, shower tray or outside gully. Stop using toilets, sinks, baths and showers. Do not run the washing machine or dishwasher, and check that nobody else in the house has one part-way through a cycle, because a discharge midway through will empty thirty or forty litres straight into the blockage. If a toilet has already been flushed and is filling, lift the cistern lid and hold or tie up the float to stop it refilling.

Protect the area at the lowest point

Work out where waste water will surface - typically the lowest fixture in the house or the nearest outside gully - and clear the area around it. Move rugs, boxes, and anything absorbent or valuable. If waste water is already coming up, towels and a bucket contain more than people expect, and moving things out of the way now is far easier than cleaning them afterwards. If it is coming up outside, make sure it is not running towards an airbrick, a cellar light well or a door threshold.

Find and open the inspection chambers

If you can safely lift the chamber covers on your property, do it. It tells the engineer where the blockage is before they start, which saves time and therefore money, and in some cases relieves pressure on the system. Lift with a proper key or a bar rather than by hand, and take care with older cast covers, which can be heavy and can have degraded edges. Note which chambers are full and which are running clear - that is the information worth having ready when the engineer arrives. Do not attempt to reach into a chamber.

What not to do

Do not pour chemical drain cleaner into a standing blockage. It will not clear a serious obstruction, and it leaves a caustic pool that is a genuine hazard to whoever works on the drain afterwards - tell the engineer if you have already used any. Do not try to rod a drain with garden tools or improvised rods; rods that come apart in a pipe turn a clearance into an excavation. Do not lift a chamber cover you cannot manage safely, and do not leave one open and unattended, particularly with children or pets around. And do not put a hose into a chamber to flush the blockage, which usually just fills the system further.

If waste water has entered the property

Treat it as contaminated. Keep children and pets away from it, wear gloves, and wash hands thoroughly afterwards even if you think you avoided contact. Photograph the affected area and anything damaged before you start clearing up - if this becomes an insurance claim, that record is what supports it. Ventilate the area. Once the drain is cleared, hard surfaces need disinfecting; carpet and underlay affected by foul water usually cannot be salvaged and should be assessed rather than simply dried out.

Common questions

Should I call Thames Water or a private firm first?

If more than one property is affected, or if every chamber on your land is full and backing up, call Thames Water first - the blockage is likely on their lateral drain or public sewer and they will clear it free of charge. If the problem is clearly confined to your property, a private firm will be faster. Our guide on drain responsibility explains how to tell.

Is a backing-up drain a health risk?

Foul water carries bacteria and should be treated as contaminated, so avoid contact, keep children and pets clear, and wash thoroughly afterwards. It is not usually an emergency in the medical sense, but it is a reason to stop using the drainage and get it cleared rather than living with it.

Can I just wait until the morning?

If nothing is backing up into the property and you can avoid using the drainage overnight, usually yes, and it will cost less than an out-of-hours callout. If waste water is entering the property, or the only toilet in the house is unusable, that is worth calling out for.