Carbon monoxide warning. If your carbon monoxide alarm goes off, or you notice a lazy yellow or orange flame, soot or staining around the boiler, or feel headaches, dizziness or nausea that ease when you're away from home: turn the boiler off, open windows, get outside and call the National Gas Emergency Service on 0800 111 999.
Banging, or a kettle-like rumble
Often called kettling. It's usually caused by limescale or sludge building up in the heat exchanger, which makes water overheat and boil in places. It can also come from low pressure or a pump problem. Kettling won't fix itself and makes the boiler work harder, so get an engineer to look at it.
Gurgling
- Air in the system. Bleed your radiators, then check the pressure.
- Low pressure. Check and top it up.
- A frozen condensate pipe, if it's freezing outside. How to thaw it.
Whistling
Often the same cause as kettling: limescale or sludge restricting the flow. It can also be low pressure. If topping up the pressure doesn't stop it, call an engineer.
Humming or vibrating
Can come from the pump running too fast or a loose part. A pipe vibrating against a wall or floor is often harmless, but an engineer should check the boiler itself.
Clicking without lighting
If the boiler clicks repeatedly but doesn't fire up, it may be struggling to light. That's often down to the gas supply or a frozen condensate pipe. See our guides to ignition fault codes on the boiler help page.
Never take the casing off your boiler or try to repair gas parts yourself. That work must be done by a Gas Safe registered engineer. With boiler cover, your provider sends one for you. Compare boiler cover.
Have boiler cover?
Call your provider before paying an engineer yourself. A repair like this is exactly what cover is for.
No cover yet? A new plan won't pay for a fault you already have, because problems that exist when you join aren't covered and there's a waiting period at the start. It can protect you next time.
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Last updated 30 October 2026