Boiler·5 Jul 2026 · 4 min read
By Mohammed Miah, Gas Safe registered heating engineer
Boilers are meant to run quietly. A new or unusual noise is normally worth paying attention to, the type of sound is a good clue to what's causing it.
Common noises and what they usually mean
- Banging or 'kettling', often sludge or limescale build-up around the heat exchanger, causing water to boil locally and make a kettle-like noise.
- Gurgling, usually trapped air in the system, or occasionally a problem with the condensate pipe.
- Whistling, often caused by low water pressure or a partially closed valve restricting flow.
- Humming or vibrating, can point to a failing pump or a component working loose.
- Clicking on startup, often normal, but a persistent or loud click can indicate an ignition issue.
A single quiet click at startup usually isn't a concern. Loud, repeated, or new noises are worth getting checked, particularly banging or kettling, since it can point to a system that needs a system flush before the problem gets worse.
