From the Silverdale blogWhy is my boiler making a loud noise?
Banging, humming, gurgling or whistling — each boiler noise means something different. Here is how to tell what yours is trying to say.
From the Silverdale blogBanging, humming, gurgling or whistling — each boiler noise means something different. Here is how to tell what yours is trying to say.
A bit of quiet humming is normal. A loud bang, whistle, gurgle or vibration is your boiler telling you something is wrong — and the type of noise is a surprisingly good clue to what.
Banging or whistling — often called kettling — is the big one. It happens when limescale builds up on the heat exchanger and water gets trapped in a restricted space, overheats and effectively boils, just like a kettle. In hard-water areas like West London this is common, and it is worth taking seriously: kettling puts the boiler under strain and should be checked by a Gas Safe engineer.
Gurgling usually means trapped air in the system. If it is coming from your radiators too, bleeding them often clears it — a job you can safely do yourself. If it keeps coming back, air is getting in somewhere and it is worth a look.
Humming tends to come from water moving too fast or under too much pressure — sometimes the mains pressure is high, sometimes the pump is set too fast, sometimes it is the fan bearings. Vibrating or rumbling often points to an unbalanced system or, again, sludge and debris restricting flow through the heat exchanger.
The common thread with the worst noises — banging, kettling, persistent vibration — is limescale and sludge, which is exactly what our hard water produces. A powerflush clears the build-up and an annual service keeps it from coming back.
A thermostat that has stopped reading temperature accurately will make the boiler fire and shut down far more often than it should, and that constant cycling is noisy. So is pipework that has worked loose or was never properly clipped and insulated: as pipes heat up they expand, and if there is nothing holding them they knock against joists and walls. Both are easy to fix once identified and both get blamed on the boiler unfairly.
If there is a code on the display alongside the noise, it narrows things down quickly. Codes differ between manufacturers, so always check yours against the make, but the ones we see most often alongside noise are F28 and F29 for ignition failure and ignition lockout, which can produce banging or repeated clicking as the boiler tries to light. F22 and F75 relate to water pressure being too low or outside its normal range. F61 and F63 point at the fan and the air pressure switch. F85 indicates a flame sensor fault. Our guide to boiler fault codes goes through how to read them.
One often overlooked factor contributing to noisy boilers is improper system sizing. If the boiler or radiators are too small for your home, they may work harder, leading to increased noise. Undersized boilers can cycle frequently, wasting energy and causing wear and tear. At Silverdale Plumbing, I stress the importance of proper system sizing to minimise noise. By assessing your home's needs, I recommend appropriately sized equipment and offer advice on insulation improvements. My goal is to provide effective solutions for quieter, more efficient heating.
Chris Barton, owner of Silverdale Plumbing & Heating
If your boiler is banging, whistling or vibrating loudly, don't ignore it — call us on 020 3355 0998. We cover West London and can find out exactly what is causing it.
A gentle hum is normal, but loud banging or whistling — known as kettling — shouldn't be ignored, as it means the boiler is overheating internally and should be checked by a Gas Safe registered engineer. Gurgling from trapped air is less urgent and can often be fixed by bleeding your radiators.
Kettling is the banging or whistling sound a boiler makes when limescale builds up on the heat exchanger, trapping water that overheats and boils like a kettle. It is common in hard-water areas like West London and is usually solved with a powerflush and descale.
Gurgling is normally trapped air moving through the system. If your radiators gurgle too, bleeding them often fixes it. If the noise keeps returning, air is getting in somewhere and it is worth having the system checked.
Often, yes — if the noise is caused by sludge or limescale restricting flow (banging, kettling or vibrating), a powerflush clears the build-up and usually quietens the system down. We will confirm the cause first so you only pay for what actually fixes it.
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