A noisy boiler isn’t just annoying—it can be a sign of a deeper problem. Whether it’s banging, whistling, or humming, understanding why your boiler makes noise can help you fix the issue before it gets worse (or more expensive).
In this guide, we’ll explain what different boiler noises mean, what causes them, and what you should do about it.
Common Boiler Noises and What They Mean
1. Banging or Knocking
Often caused by kettling—when limescale builds up inside the heat exchanger and restricts water flow. This leads to overheating and loud banging noises.
2. Whistling (Like a Kettle)
Another sign of kettling. Trapped air or limescale can cause water to boil unevenly, leading to that whistling sound.
3. Humming or Vibrating
Could be loose components or a pump running at the wrong speed. It’s less urgent but still worth checking.
4. Gurgling
Often due to trapped air in the system. Bleeding your radiators might fix it.
5. Clicking or Tapping
Can happen as metal pipes expand or contract with heat, but if it’s persistent, it may be an ignition issue.
Is a Noisy Boiler Dangerous?
Not always—but it can be. For example, kettling from limescale can damage your boiler over time. Faulty ignition or pump issues can also lead to system failure if ignored.
If your boiler is new and still under warranty, contact the installer. If it’s old or hasn’t been serviced in a while, it’s time to call a Gas Safe engineer.
How to Fix a Noisy Boiler
Here’s what you can try before calling in the pros:
- Bleed the radiators to remove trapped air
- Check boiler pressure—low pressure can cause strange noises
- Inspect for leaks or obvious loose fittings
But avoid opening the boiler casing yourself. If in doubt, get a professional.
Preventing Boiler Noise Long-Term
- Annual servicing catches problems before they get worse
- Install a magnetic filter to reduce sludge buildup
- Use limescale inhibitors if you live in a hard water area
Should I Repair or Replace a Noisy Boiler?
If your boiler is over 10 years old and frequently making noise, it might be cheaper to replace it. A new boiler will run quieter, be more efficient, and save you money on repairs and bills.
FAQs
What causes a boiler to make a banging noise?
Usually kettling caused by limescale buildup in the heat exchanger. It restricts flow and causes overheating.
Why does my boiler whistle like a kettle?
Trapped air or limescale can cause uneven water heating, leading to whistling sounds.
Is it dangerous if my boiler makes noise?
Not always, but it could be. Noises can indicate issues that may lead to a breakdown or safety concern.
What should I do if my boiler is noisy?
Try bleeding radiators, checking pressure, and inspecting for leaks. If that doesn’t help, call an engineer.
Why is my boiler humming constantly?
Likely due to pump settings or loose parts. It’s not urgent but should be checked.
Can air in the system cause boiler noise?
Yes, air trapped in the radiators or pipework can create gurgling or banging noises.
How do I bleed my radiators?
Turn off the heating, open the bleed valve with a key until water comes out, then close it. Recheck pressure after.
Should I turn off my boiler if it’s making noise?
If the noise is loud or sudden, it’s safer to turn it off and call a professional.
Can a noisy boiler increase energy bills?
Yes, inefficiencies like kettling make your boiler work harder and waste energy.
How much does it cost to fix a noisy boiler?
It depends on the issue—bleeding air is free, while replacing a pump or heat exchanger can cost £150–£500.
