Experts are telling people to be aware of the smells, which could mean they are in danger of a failure. If you smell one in particular, you need to leave the property immediately.

Stephen Day, heating engineer and operations director at iHeat said: "Whilst there are multiple signs pointing towards possible issues with a boiler, unusual smells can be a key indicator, but they're often dismissed. Strange odours are some of the most common early signs of a faulty boiler, often requiring urgent attention from an engineer, so it's crucial to know what smells to take seriously." The most dangerous smell is that of sulphur which can smell like rotten eggs.

This pungent smell is typically associated with a , which can be a major hazard and needs to be dealt with right away.

Stephen said: "If you do get a whiff of egg, immediately shut off the boiler and gas supply, leave your property and call the Gas Emergency number on 0800 111 999."

Another common warning smell is an oily, or plasticky smell. This is often due to a motor or pump overheating, which can become a fire hazard if neglected.

If you smell this scent, you should turn your boiler off, unplug it (if possible), and call out a Gas Safe engineer as soon as possible.

If the area around your boiler has a musty or mouldy smell, you may have mould or mildew growing within your boiler or water damage around it.

While this may not be as dangerous as a gas leak, you shouldn't wait to rectify the issue. If left, mould and mildew can cause long-term damage to your boiler's components and increase serious health risks, so as soon as you find the culprit, treat it right away.

A smell of burning hair could indicate an issue with the metal coil found inside your boiler.

When dust, debris, hair or other particles come into contact with this coil they will start to burn, resulting in a burning smell that can smell like burnt toast or burning hair.

While this is usually no cause for alarm and is expected from time to time, if the smell doesn't go away within half an hour or it keeps coming back, it may signal an issue with the air filter or furnace burner.

If this is left and the filter isn't changed, it can quickly become a fire risk.

However, there is one risk that has absolutely no smell at all, which makes it hard to figure out.

Carbon monoxide is the most dangerous sign of a faulty boiler and is colourless and odourless - it's so dangerous this gas is often referred to as 'the invisible killer'.

Since you cannot detect CO by smell, it's crucial to be aware of the symptoms of carbon monoxide poisoning, which include headaches, dizziness, breathlessness, nausea, collapsing, and loss of consciousness.

If you or anyone in your household experiences these symptoms, you should immediately turn off the boiler, open windows for ventilation, and seek medical attention.

Installing a carbon monoxide detector near your boiler is also a vital safety measure, as it can alert you to the presence of this dangerous gas before it poses a serious health risk.