Guide · Central heating
Radiators are rarely silent, but a new or loud noise usually means something specific. Here's how to tell gurgling from banging from ticking, and which ones you can sort yourself.
A gurgling radiator, often with a cold patch at the top, usually has air trapped inside. Air rises and collects at the top of the radiator, and the water trickling past it makes the noise. The fix is to bleed the radiator with a key — our how to bleed a radiator guide walks through it — and then check the boiler pressure afterwards.
A loud bang when the heating comes on or off is often pipes expanding and contracting against floorboards or joists as they heat and cool. It's annoying rather than dangerous, and clipping or insulating the pipes where they rub usually quietens it.
Knocking can also come from a pump set too high, pushing water round faster than the system wants, or from sludge restricting flow. If the banging is new, loud or getting worse, it's worth having the system looked at rather than just turning the radio up.
Light clicking or ticking as the heating warms up or cools down is the sound of metal expanding and contracting — radiators, pipes and valves all do it. If it's always happened and hasn't changed, it's nothing to worry about. A sudden new loud clicking from one radiator valve can mean a valve starting to stick, which is a cheap part to replace.
A brief hiss when you open a bleed valve is air escaping, which is what you want. A radiator that hisses continuously, or whistles, may have a valve that's nearly closed forcing water through a tiny gap. Opening the valve fully, or having the system balanced so no radiator has to be throttled right down, usually stops it.
Noise from a radiator when the heating is off is usually cooling metal contracting, which is normal. If you hear water movement when everything is off, the pump may be overrun or a valve may be letting water circulate when it shouldn't. Note when it happens and mention it when you call — the timing is a useful clue.
Sometimes a noise that seems to come from the radiators is actually travelling from the boiler through the pipework. A rumbling or kettling sound points to the boiler rather than the radiators — our boiler making noise guide covers those sounds, and boiler kettling explains the rumble in detail.
Persistent banging, knocking or gurgling that bleeding doesn't fix usually means the system needs balancing, cleaning or a pump check. That's part of our central heating work, and a power flush can help where sludge is the cause. Send the quote form with a description of the sound and when it happens.
Common questions
Clear answers before you arrange a visit.
Almost always trapped air. Bleed the radiator with a key, then check the boiler pressure and top it up if needed.
Usually not — it's often pipes expanding against woodwork. But new, loud or worsening banging is worth having checked in case the pump or sludge is involved.
Metal expanding as it warms. Light ticking that has always happened is normal; a sudden change in the sound is worth a look.
Yes. Sludge restricts flow and can cause knocking and gurgling. If bleeding doesn't help and the water runs black, the system may need cleaning.
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