A foul-smelling boiler is a sure sign that something’s wrong. It might be a straightforward fix or a complex problem, but at its worst, it could be a gas leak which needs urgent attention.
In this blog, we’ll look at what could be causing your boiler to smell and what to do about it.
Boiler smells and their causes
Boiler smells should always be investigated by a Gas Safe registered engineer. If the smell is accompanied by gurgling, banging, or whining, it’s a sign your boiler is on its way out, and it could be time for a new boiler.
Read more: When to replace your boiler – 6 signs you shouldn’t ignore.
My boiler smells like rotten eggs
The smell of sulphur or rotten eggs needs urgent attention.
The gas in your boiler is naturally odourless, so mercaptan is added to make detecting a gas leak easier. Mercaptan is an organic sulphur compound with a distinctive smell, similar to rotten eggs.
This smell is a sign of a gas leak, and you should act quickly.
What to do if you think you have a gas leak
- Open all the doors and windows to allow air to circulate through the property.
- Turn off the gas if it’s safe to do so (you’ll find the mains tap near the gas meter).
- Evacuate the property and inform your neighbours.
- Call the National Gas Emergency Service on 0800 111 999.
What NOT to do if you think you have a gas leak
- DO NOT smoke or light a flame.
- DO NOT use any electrical appliances.
- DO NOT turn lights or power switches on and off.
Only Gas Safe registered engineers can assess and fix a natural gas boiler. Don’t attempt to do anything yourself.
A musty or mouldy smell
A mouldy smell can indicate a problem with the water drainage in your boiler. An unnoticed water leak or excessive moisture around your boiler is the ideal environment for mould and mildew to grow.
Mould and mildew pose a health risk, especially in the very old and young and anyone with a weakened immune system or a respiratory illness.
You can remove mould with special cleaning agents but should also tackle the underlying problem to prevent it from returning. Contact a local plumber who can diagnose and fix the issue.
In the meantime, ensure there is enough ventilation around your boiler to reduce humidity and prevent the build-up of condensation.
Melting plastic or burning smell
The smell of burning or melting plastic is a common boiler complaint. It typically indicates an electrical fault or an overheating component, such as a motor bearing.
Overheating usually occurs when limescale or mineral deposits build up in the system and go unchecked. It means your boiler has to work harder to maintain its temperature, which can lead to kettling. This is where the water inside the boiler overheats, producing a burning smell and a gurgling or rumbling sound similar to a boiling kettle (hence the name).
Your heating engineer will descale your boiler and, if necessary, flush out the entire system using high-powered water jets and cleaning chemicals to remove the debris and sludge.
Prevention tips
To prevent a build-up of limescale in your system, consider the following:
- Add a magnetic filter to your boiler to help collect rust and debris.
- Ensure the water pressure in the boiler is at the recommended level to maintain proper flow.
- Regularly inspect the system for leaks or trapped air that could disrupt water flow.
Why does my water smell like rotten eggs?
If your hot water smells like rotten eggs, there could be bacteria in your system. Anaerobic bacteria can cause the water to smell like sulphur or rotten eggs (much like the eggy smell you get when there’s a gas leak).
It’s often caused by setting your boiler temperature too low. To kill off the bacteria in the water, the temperature must be at least 60 ℃. Setting your boiler below 60°C increases the risk of Legionella bacteria forming, which can cause a severe form of pneumonia known as Legionnaire’s disease.
Read more: What temperature should my boiler be?
Leaving your boiler unused for long periods of time, in empty properties, for example, can also cause bacteria to form.
A heating engineer can kill off the bacteria with a chemical flush that uses chlorine dioxide (in high-risk or severe cases) and replace parts that have been affected. To reduce the risk of it happening again, ensure your boiler temperature is above 60℃ and run showers and taps that aren’t often used.
Is it normal for a boiler to smell?
It’s not usual for a boiler to smell. Whether it’s rotten eggs, burning, or a mouldy smell, you should have it looked at by a Gas Safe registered engineer. Your local engineer will be able to diagnose the underlying cause and give you a price to fix it.
Important note: It could be a gas leak if your boiler gives out a sulphuric or eggy smell. You must act immediately to prevent ill health or a fatality from severe gas exposure.
Symptoms of early gas poisoning, especially from carbon monoxide, often resemble the flu or food poisoning. Children, the elderly, and people with pre-existing health conditions (like heart disease) are more vulnerable to the effects of gas poisoning.
Call the National Gas Emergency Service on 0800 111 999 (available 24/7) if you suspect a gas leak.
How do I get rid of the smell in my boiler?
Tackling the underlying cause of your boiler’s smell is the best way to deal with it. Covering up the smell can be dangerous, but it can also make the problem worse, costing you more money in the long term.
Call your local Gas Safe registered engineer. We’ll diagnose the problem efficiently and safely, give you a price to fix it and arrange to do the work. Our engineers have seen (and smelt) every type of boiler problem – no problem is too big or too small.
