Boilers make some noise. Some of it is normal and some of it is telling you something.
Banging or rumbling, like a kettle
This is the common one, and it’s usually called kettling.
Over time, limescale and sludge can build up inside the heat exchanger, which is the part where the flame heats the water. When enough has collected, the water can’t flow through properly, so it overheats and boils. The banging is steam forming and collapsing.
It isn’t usually dangerous, but it’s not something to live with either. A boiler that’s kettling is working harder than it should and wearing itself out faster.
Gurgling
Often air in the system. If radiators are cold at the top and warm at the bottom, bleeding them frequently sorts the gurgling too. If it keeps coming back, air is getting in from somewhere.
Whistling
Can be the same cause as kettling (poor flow), or a pump running harder than it needs to, or a valve that’s partly closed.
Clicking when it fires up
A few clicks as the boiler lights is the ignition, and that’s normal. Clicking that goes on and on without the boiler lighting is worth getting looked at.
Humming or vibrating
Frequently the pump. Sometimes it’s just passing vibration into a wall, which is annoying but harmless. Sometimes the pump is on its way out.
When to turn it off
Turn the boiler off and get someone out if:
- You smell gas. Call the National Gas Emergency Service on 0800 111 999, not a plumber
- Water is leaking from the boiler itself
- Loud banging started suddenly rather than creeping up over months
- The boiler keeps locking out and needing a reset
The rest is worth booking in, without panicking about it.
Last updated September 2026
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