A dusty or slightly burnt smell for the first few hours after you switch your heating back on is normal. Dust settles on radiators, pipes and inside the boiler over the summer, and it warms up and drifts into the room once the heating runs again. It should fade within a day or so.
Other smells are a different matter. This post explains which smells are harmless, which point to a fault, and which mean you should turn the boiler off straight away. You can check a few things safely yourself, but never remove the boiler casing or try to trace a gas smell on your own.
Why a dusty smell is normal at first
Over the warmer months your radiators sit cold, and dust, pet hair and fluff settle on the top and between the fins at the back. The same happens on pipework and around the boiler. When hot water flows through again, that dust warms up and gives off a faint, toasty smell.
It tends to be strongest in rooms that have been shut up for a while, such as a spare bedroom, and behind radiators with a cover or a shelf above them.
How long the smell should last and how to help it clear
A dust smell usually fades over the first day of heating, and rarely lasts beyond two or three. To help it along:
Turn off the heating and let the radiators cool, then vacuum along the top and underneath each one with a narrow nozzle.
Use a long radiator brush to clear dust from between the fins.
Move anything resting on or against a radiator, such as clothes, curtains or toys.
Open a window for an hour while the heating first runs.
If the smell gets stronger rather than weaker, or it comes from the boiler itself rather than the radiators, treat it as a fault and read on.
An eggy smell when you bleed a radiator
Bleeding a radiator means opening the small valve at the top to let trapped air out. Sometimes the air that hisses out smells of rotten eggs. This is usually gas made inside the system as the steel radiators slowly corrode, mixed with sludge in the water. It is a sign of a dirty system rather than a gas leak.
Keep flames and cigarettes well away while you bleed, as some of that trapped gas can catch light. Close the valve as soon as water appears, and the smell should go within minutes. Our guide on how to bleed a radiator walks through it step by step.
If you need to bleed radiators often, or the water that comes out is black, the system is likely full of sludge. A powerflush, which is a deep clean of the radiators and pipework with water and cleaning chemicals, may be the answer.
If the eggy smell is anywhere else in the house, or doesn't clear once the valve is closed, treat it as a gas smell.
A burning plastic, electrical or fishy smell
A sharp smell of hot plastic, or an odd fishy smell, can come from overheating electrics. On a heating system that might be the pump, the wiring to the boiler or the controls. It can also be something touching a hot pipe or the boiler flue, which is the pipe that carries fumes outside.
Check nothing has fallen behind a radiator or onto the boiler. If the smell is coming from the boiler, the pump or a control box, switch the heating off at the boiler's isolating switch and don't use it again until a qualified engineer has looked at it. Never open the boiler casing or the cover of an electrical fitting.
If you smell gas
Mains gas has a smell added to it, often described as rotten eggs, so that leaks are easy to notice. If you smell gas anywhere in your home:
Don't use light switches, plugs, doorbells or anything with a flame.
Open doors and windows.
Turn off the gas at the meter if you can reach it safely, using the lever next to it.
Leave the house and call the National Gas Emergency Service on 0800 111 999 from outside.
The emergency service makes the supply safe. After that, a Gas Safe registered engineer needs to find and repair the leak before the gas is turned back on. One of our customers found this out first hand: "I required a boiler service check which was all ok. Then the engineer found we had a gas leak."
Fumes, soot and carbon monoxide
Carbon monoxide is a poisonous gas that a faulty boiler or gas fire can give off. It has no smell, no colour and no taste, so you can't rely on your nose to find it. A smell of exhaust fumes near a boiler is still a warning, because it means fumes are escaping where they shouldn't.
Other signs to look for are black or brown staining on or around the boiler, a lazy yellow or orange flame on a gas appliance instead of a crisp blue one, and more condensation on windows than usual. Headaches, dizziness, sickness or tiredness that ease when you go out can also be a sign.
If you notice any of these, turn the appliance off, open windows, get everyone into fresh air and call 0800 111 999. If anyone feels unwell, get medical help. Every home with a gas boiler should have an audible carbon monoxide alarm, tested regularly.
