Why do my radiators bang and gurgle?

Different noises mean different things, and the noise itself is the diagnosis.

Gurgling or trickling almost always means air in the system. Air rises to the top of a radiator, and water moving past it produces the sound. The fix is bleeding: turn the heating off and let it cool, open the bleed valve at the top with a radiator key until the hissing stops and water appears, then close it. If radiators need bleeding repeatedly, air is getting in — usually a small leak, a faulty automatic air vent, or corrosion producing hydrogen gas inside the system, which is worth investigating.

Banging or knocking, sometimes called kettling, is usually limescale or sludge in the boiler heat exchanger. Deposits create hot spots where water flashes to steam and collapses, producing a sound like a kettle boiling. In hard-water areas this is common. It needs a power flush and often an inhibitor or scale reducer fitted — and it shortens boiler life if ignored.

Ticking and creaking during warm-up and cool-down is normally metal expanding against its brackets or pipes rubbing against joists. It is harmless. Loosening an over-tight pipe clip or packing felt where a pipe passes through timber usually stops it.

A humming or vibrating noise generally comes from the circulation pump — often the speed setting is too high, or the pump is failing.

Cold at the bottom, warm at the top is the opposite of an air problem: that is sludge settling in the base of the radiator, and it needs flushing rather than bleeding.

Check system pressure after bleeding; it usually drops and may need topping up.