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Blocked Kitchen Sink: How to Clear It and When to Call a Plumber

Blocked water pooled in a London kitchen sink

A blocked kitchen sink is usually a build-up of grease and food waste in the trap or waste pipe just below the plughole. Most of the time you can clear it with a plunger, then a cleaned U-bend. If the water will not move after that, or other drains in the house are slow too, the blockage is deeper and needs a drainage engineer.

This guide covers why kitchen sinks block, how to clear one in a sensible order, how a blocked bathroom sink differs, and the signs that mean you should stop and call someone.

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TL;DR

  • Grease, soap scum and food scraps are the usual causes of a blocked kitchen sink, and they combine into a sticky sludge inside the pipe.
  • Start with a plunger, then a drain unblocker, then clean the U-bend with a bucket underneath. This is the order Which? recommends.
  • If only one sink is slow, the problem is probably in or near that plughole. If several fittings are slow or water backs up elsewhere, the problem is further down the system.
  • Call a plumber when your own attempts fail, when the water smells or comes back up, or when more than one drain is affected.

Table of Contents

Why a kitchen sink blocks

A kitchen sink takes a mix of hot water, fat, food and detergent. That mix is the reason it blocks more often than most other fittings.

WaterSafe Register names grease as one of the most common culprits. Cooking oils and fats run down while warm, then cool and harden on the pipe wall, so the channel narrows with each wash-up. Food remnants such as coffee grounds, pasta, rice and small scraps catch on that coating. WaterSafe says food particles mixed with grease and soap can form a thick, sticky sludge.

That explains the typical pattern. The sink does not stop all at once. It drains a little slower each week, then one day a pan of water sits there.

The usual suspects in a kitchen are:

  • Fat, oil and grease from roasting tins, frying pans and the last of the gravy.
  • Coffee grounds, which pack down rather than wash away.
  • Rice and pasta, which swell in water and settle in the bend.
  • Soap scum and washing-up residue, which bind the rest together.
  • Wipes and similar items. Thames Water warns that wet wipes cause blockages, even those labelled flushable. They belong in the bin, not in a sink or toilet.

Before you start: what to check first

Two quick checks save time and tell you how serious the problem is.

Is it just this sink? Run the bathroom taps, flush the toilet and watch the washing machine or dishwasher drain. David Wilson Homes explains that if only one fitting is not draining properly, the blockage is probably in or near that specific plughole. If fittings in different rooms are affected, the problem could be the main outflow from the house.

Two checks for diagnosing a blocked sink

Is the water standing, or just slow? Slow drainage suggests a partial blockage that is still within reach of a plunger. Standing water that does not move at all is a full blockage, so you will need the U-bend step below, or professional help.

Get ready with rubber gloves, a bucket, an old towel, a washing-up bowl and a torch. Remove any dishes and scoop out as much standing water as you can into the bucket.

How to unblock a kitchen sink, step by step

Work from the least messy method to the most. Stop as soon as the water runs freely.

1. Use a plunger

Which? advises starting with a plunger and making sure there is enough water to cover the cup. The water is what transmits the pressure, so a dry cup does very little.

  1. Block the overflow hole with a damp cloth. If you have a double sink, block the second plughole too, otherwise the pressure escapes.
  2. Place the plunger over the plughole so the cup is fully covered with water.
  3. Push down and pull up firmly in a steady rhythm for 20 to 30 seconds.
  4. Pull the plunger away sharply and see whether the water drops.

Repeat a few times. A sink plunger works best if you keep it for sinks only, not the toilet.

2. Try a drain unblocker

If the plunger does not do it, Which? suggests a drain unblocker next. Follow the instructions on the bottle exactly: check it is suitable for your pipework, wear gloves, keep the room ventilated and never mix products. Never use a chemical unblocker and then plunge straight afterwards, because the liquid left in the sink can splash back onto your skin and eyes.

3. Clean the U-bend

If the sink is still blocked, Which? says to unscrew and clean the U-bend with a bucket underneath to catch the water and debris. David Wilson Homes also notes that the trap can usually be unscrewed or unclipped, removed and cleaned.

  1. Put the bucket under the trap and lay the towel around it.
  2. Unscrew the two large nuts, by hand if you can, otherwise with a wrench wrapped in cloth to protect the finish.
  3. Lower the trap carefully. Expect dirty, smelly water.
  4. Empty it into the bucket and clear the sludge with an old brush or a gloved hand.
  5. Look into the pipe stub on each side with a torch and clear what you can reach.
  6. Refit the trap, tightening the nuts snugly but not excessively, then run the tap and check for drips.

Most kitchen blockages end at this step because the trap is where fat and food settle first.

4. Stop and call for help

If the trap is clear and the water still will not go down, the blockage is further along the waste pipe. Pushing coat hangers or rods into the pipe tends to compact the blockage or damage the joints. This is the point to hand over.

A quick guide to what you are seeing

What you notice Likely location What to do
Kitchen sink slow, other drains fine Plughole, trap or short waste pipe Plunger, then clean the U-bend
Water in the trap, but trap and pipe are clear Further along the waste pipe Call a drainage engineer
Kitchen sink and dishwasher or washing machine both slow Shared waste pipe in the same room Call a plumber
Sink slow and a bathroom fitting or toilet also affected Main outflow from the house Call a plumber promptly
Water or smells coming back up through the sink Wider drain or sewer problem Call a plumber, and the water company if the problem is outside your boundary

The last three rows follow what David Wilson Homes says: multiple fittings in the same room point to a shared waste pipe, and fittings in different rooms point to the main outflow.

What about a gurgling sink that is not blocked?

A gurgle is air struggling to get through water. It often means a partial blockage that is restricting flow, so the sink has not quite stopped but is not draining cleanly either. It can also point to a problem with how the waste pipe is vented, particularly if the noise happens when another fitting, such as the washing machine or toilet, empties.

Treat a persistent gurgle as an early warning. Clean the trap and plunge as above. If the gurgle comes back, or happens alongside slow drainage in other rooms, ask a plumber to look at the pipework rather than waiting for a full blockage.

What about a gurgling sink that is not blocked?

Should you pour boiling water down a blocked sink?

People ask this more than almost anything else, and it is understandable: a kettle is to hand and costs nothing. The methods Which? lists as the sensible sequence are the plunger, an unblocker and the U-bend, and we would follow that order. A kettle of water can also scald you when it splashes back from a full sink, so keep it away from a plunger session and away from children. If the sink is plastic, check that hot water is suitable before you try it.

Blocked bathroom sink: a different cause, the same method

Bathroom sinks block with a different mix. Which? says bathroom drains typically clog with hair, soap scum and non-biodegradable materials, and that a plunger is again the first thing to try. It adds that unblockers designed to dissolve hair and soap scum are particularly effective: one Best Buy in its tests shrank two large hairballs within 15 minutes.

To clear a bathroom sink:

  1. Remove the pop-up plug if there is one. Hair often wraps around it.
  2. Plunge with the overflow blocked, as for the kitchen.
  3. Use a hair and soap unblocker suited to your pipes if the plunger does not work.
  4. Clean the trap under the basin with a bucket underneath. These traps are small, so water spills fast.

A slow bathroom sink with a clear trap, or a bathroom sink that is blocked at the same time as the bath or toilet, is a call for a plumber rather than another attempt.

Signs that the problem is bigger than the sink

Some blockages are not really about the sink at all. Look out for:

  • More than one fitting affected. Different rooms suggest the main outflow. The same room suggests a shared waste pipe.
  • Water backing up. Thames Water explains that when wastewater cannot flow away it can come back up through a toilet or sink and flood your home.
  • A smell that does not clear once the trap is cleaned.
  • Gurgling in several drains at once.
  • A blockage that returns within days of being cleared.

If the water is coming back into the house, stop using the water, keep children and pets away and call a plumber straight away. If you are unsure whether the blockage sits in your own pipes or the public sewer, Thames Water advises contacting a plumber if you think the blockage is within your drains or sewer. It also notes that some home insurance and home protection policies include drainage cover, so check your policy before you book.

Why a drainage engineer can fix what you cannot

When a blockage sits beyond the trap, the tools change. Which? quotes a drainage expert who says specialists may use cameras or sonic tracking devices to find deeper blockages and high-pressure jets to clear them, and that you should not attempt this yourself. A camera shows what the blockage is and where it sits, so the fix is targeted rather than guesswork.

If you are in London, our drain unblocking service covers exactly this kind of job. We also work by area, for example in Fulham, Chiswick, Wandsworth and Kensington.

Our perspective

Most kitchen sink callouts we hear about begin the same way: the sink was slow for weeks, someone tried a bottle of unblocker, then the sink stopped on a Sunday evening with guests due.

Our view is simple. A first attempt with a plunger and a cleaned trap is reasonable for a single slow sink. The moment it fails, or the problem touches more than one fitting, it is quicker and less stressful to bring in an engineer than to keep experimenting at the pipework.

That is why we run calls 24/7 and quote every job at a fixed price before work starts. You know what you are agreeing to before anything is opened up, and there are no surprise costs on the day. Our engineers are Gas Safe registered, which matters when a kitchen job touches the boiler or a gas appliance nearby.

For households, landlords and businesses alike, a blocked kitchen is not only an inconvenience: it stops cooking, washing up and, in a commercial kitchen, trading. A fast answer and a clear price are the best protection against that.

the author

Need a plumber for a blocked sink?

If the plunger and the U-bend have not worked, or you would rather not take the pipes apart, we can help. Our engineers clear blocked kitchen and bathroom sinks and drains across London, around the clock, and each job is quoted at a fixed price before work begins. If the blockage turns out to be a leak, a damaged pipe or something that needs a wider repair, we can deal with that on the same visit through our plumbing work service.

Evoplumbers

For out-of-hours situations, our Emergency Call Out page explains how we respond, and our guide to what to do and who to call at night covers the first steps. You can see everything we do on our plumbing services in London page.

How to stop it happening again

Prevention is mostly habit, and it costs nothing.

  • Keep fat out of the sink. David Wilson Homes recommends pouring cooking grease into a container to cool, then putting it in the bin. The same applies to coffee grounds and other solids.
  • Scrape plates into the bin before washing up, and use a sink strainer to catch scraps.
  • Bin your wipes. Thames Water’s three Ps rule says only pee, poo and toilet paper go down the toilet, with everything else in the bin.
  • Treat a slow sink early. A quick clean of the trap now is easier than clearing a full blockage later.
  • Do not ignore a gurgle or a smell. Both are the system telling you air or water is not moving freely.

FAQ

How do I unblock a kitchen sink without a plumber?

Start with a plunger, with enough water to cover the cup and the overflow blocked. If that fails, try a suitable drain unblocker, then unscrew and clean the U-bend with a bucket underneath. This is the sequence Which? sets out. If the water still stands, call a plumber.

Why won’t the water go down my kitchen sink?

The usual reason is a build-up of grease, soap scum and food scraps in the trap or waste pipe. If only this sink is affected, the blockage is probably near the plughole. If other fittings are slow too, it is likely further down the system.

When should I call a plumber for a blocked sink?

Call when the plunger, an unblocker and a cleaned U-bend have not worked, when more than one drain is affected, or when water or smells come back up. Deeper blockages need cameras and high-pressure jets, which are not DIY jobs.

Can a blocked bathroom sink be cleared the same way?

Yes, the method is the same: plunger, hair and soap unblocker, then the trap. The cause is different, though, because bathroom sinks mostly clog with hair and soap scum. Remove the pop-up plug first, as hair often wraps around it.

Is a blocked sink an emergency?

A single slow sink usually can wait until you can book a visit. Treat it as urgent when water is backing up into the house, several drains are blocked or you cannot use the kitchen at all. In those cases, call a plumber with 24/7 cover.

Sources

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