Chimney safety guide

Signs of a Blocked Chimney, and When to Call a Sweep

How to spot a blocked flue early, what counts as an emergency, and what you can safely check yourself.

Book a chimney inspection Call 0330 133 2121

Chimney fire? Call 999

Get everyone out of the house and call 999 if you notice:

A loud roaring or rumbling noise from the chimney
Flames or sparks coming out of the top of the chimney
Thick smoke pouring from the chimney or into the house
The chimney breast getting too hot to touch

Carbon monoxide alarm going off?

Stop using the appliance, open doors and windows, and get outside. Call the Gas Emergency line on 0800 111 999, which also covers carbon monoxide from solid fuel appliances. If anyone has symptoms like headaches, dizziness or nausea, get medical help.

Don't use the stove or fire again until the chimney has been checked. For an urgent sweep, call 0330 133 2121.

1. Warning signs you can see

Most blockages give you clues before they become dangerous.

Inside the house

Soot or debris falling into the grate or onto the stove
Scratching, fluttering or chirping from the flue
Black or tar-like staining on the chimney breast or around the stove pipe
Damp patches or white salty marks on the chimney breast
Rust on the damper, stove or register plate

Outside, from the ground

Twigs or nesting material sticking out of the pot
A damaged, leaning or missing cowl
Plants growing out of the stack
Loose or missing mortar between the bricks
A stack that looks like it's leaning

Take photos. Pictures of what you've noticed help us bring the right equipment on the first visit.

2. Signs the fire isn't drawing properly

These are usually the first signs of a partial blockage.

The fire won't behave

It's hard to light, goes out quickly, burns with a lazy orange flame or makes more smoke than usual.

Smoke comes back into the room

Smoke spills out when you open the stove door, or drifts out of an open fire, even on calm days.

You're using more fuel

The stove gives out less heat than it used to, so you're burning more logs to get the same warmth.

What this usually means: a partial blockage, heavy soot or creosote build-up, or a failing cowl. A sweep and smoke test usually finds the cause.

3. Carbon monoxide warning signs

A blocked flue can push carbon monoxide into your home, and you can't see or smell it.

Symptoms in people and pets

Headaches that ease when you leave the room or go outside
Dizziness, nausea or unusual tiredness when the fire is lit
Breathlessness or sore eyes
Pets that seem lethargic near the fire

Signs in the room

A smoky smell that lingers after the fire is out
Soot marks on walls or ceilings near the fireplace
A carbon monoxide alarm that beeps on and off
Heavy condensation on the windows in that room

Stop using the fire. If anyone has symptoms while the fire is lit, put it out safely, open the windows and get medical advice. Don't relight it until the chimney has been checked. Every room with a fuel-burning appliance should have a working carbon monoxide alarm.

4. When blockages happen through the year

Book your sweep in early autumn to catch problems before the burning season.

Spring

Nesting birds

Jackdaws start building in March and April. See our bird nesting guide.

Summer

Active nests and damp

Nests are in use and can't legally be removed. Summer rain can also soak into unused flues.

Autumn

Leaves and old nests

Leaves collect in open pots, and the spring's nests are still in place. This is the best time to sweep before winter.

Winter

Soot and creosote

Heavy use builds soot and creosote fast, especially when burning wet wood.

5. What you can check yourself, and what you can't

Safe checks you can do yourself

Look at the chimney pot and cowl from the ground (binoculars help)
Check whether the damper or stove air controls open freely
Clear ash from the grate and look for fallen debris
Test your carbon monoxide alarm and replace the batteries
Write down what you've noticed and when

Leave these to a professional

Anything that means going on the roof or up a ladder
Removing birds, nests or animals
Clearing a blockage you can't reach from the fireplace
Any sign of carbon monoxide or chimney fire damage
Cracked brickwork, liners or a leaning stack

What happens when we clear a blocked chimney

Find the blockage
We sweep and, where needed, run a CCTV camera up the flue to see exactly what's there and where.
Clear it safely
Sheets down and vacuum running while we clear debris, nests or heavy soot, then sweep the whole flue.
Test and certify
A smoke test confirms the chimney draws properly again. You get a certificate and advice on stopping it happening again.