Boilers 5 min read16 March 2026
A healthy boiler hums. Anything sharper than that is telling you something, and the type of noise narrows the fault down quickly.
Kettling — a whistling, boiling kettle sound
Caused by limescale or sludge on the heat exchanger creating hotspots that boil water locally. It stresses the exchanger and shortens boiler life. The fix is a system clean, a magnetic filter and correct inhibitor dosing, or exchanger replacement if scaling is advanced.
Banging and knocking
Usually air in the system, an over-pumping circulator, or pipework expanding against a joist notch. We bleed and balance the system, check pump speed, and fix clipping where pipes are catching on timber.
Gurgling and dripping
Gurgling points to air or a partially blocked condensate. Dripping inside the casing means a leaking seal or exchanger and should be looked at promptly — water and electrics inside an appliance is not something to leave running.
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Frequently asked questions
Is a noisy boiler dangerous?
Most noises are not immediately dangerous, but kettling and internal leaks shorten the appliance's life and should be dealt with.
Will bleeding radiators stop banging?
Often yes, if air is the cause. If it returns quickly, air is being drawn in somewhere and needs investigating.
Can kettling be reversed?
Yes, in most cases, with a power flush and descaling — provided the exchanger is not already damaged.
Related reading
Power Flushing: When You Actually Need One
What Happens During an Annual Boiler Service
Boiler Repair in Glasgow: 10 Faults We Fix Every Week