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What radiator parts can radiator keys be used on?

 What radiator parts can radiator keys be used on?

Shop for Radiator Keys

Parts of a radiator Before looking at the different types of radiator keys and how they are used, it’s useful to know the different radiator fittings that they can operate. There are different radiator keys and spanners to install, remove or adjust all the radiator parts covered here.


Panel radiator showing tappings A rectangular central heating radiator has four tappings, one at each corner. Tappings are holes with internal (female) threads. They may look like short, open-ended pipes prior to fittings being screwed into them.

Externally-threaded (male) fittings that allow various adjustments to be made to the radiator are screwed into the tappings.


Valves and valve tails

Lockshield valve and thermostat valve Two of the fittings that go into the tappings are valves, which control the flow of hot water to and from the radiator.
Various radiator valve tails
Thermostatic radiator valves (TRVs), manual valves and lockshield valves are connected to the radiator tappings by a valve tail.

The valve tail screws into the tapping, then the valve is connected to the tail with what’s known as a union connection. This is a nut with an olive – a brass ring that gets compressed, forming a seal, as the nut is tightened.

Double-ended keys, Allen or hex keys, radiator spanners, universal keys, stepped ratchet keys, combination wrench/keys and tail sockets are used to remove and fit valve tails.

External hex nut on radiator valve tail Valve tails on most modern radiators have a fixed external hexagon (six-sided) or square (four-sided) nut built into them.

They can be fitted with an open ended or adjustable spanner or a socket tail driver fitted to an electric drill.

Internal hexagon type radiator valve tail However, instead of external nuts, some valve tails have internal hexagon shapes. These are secured or removed with hexagon-shaped radiator keys.
Internally lugged valve tail Some other valve tails have bayonet, or internally lugged, fittings. The lugs are small metal studs. The grooves in some radiator keys slide over the lugs and the key is turned to fit or remove the valve.
Manual radiator valve Usually, either a manual valve…
Thermostatic radiator valve ….or a TRV is fitted to one of the two bottom tappings of a radiator.
Thermostatic valve at top of radiator Sometimes, a manual valve or TRV is fitted into one of the top tappings because of the particular design of the radiator.
Lockshield radiator valve A lockshield valve – so called because it is covered by a plastic cap to prevent adjustment when not in use – is fitted to the other bottom tapping.

Whether a particular valve is fitted to the left of right side depends on the direction in which the water is to flow through the radiator.

A manual or thermostatic valve is usually the inlet, or flow, valve, and the lockshield valve is usually the outlet, or return, valve.

Removing plastic cap from lockshield valve A lockshield valve can be adjusted to increase or reduce the flow of hot water through the radiator. Removing the cap reveals the top of a spindle, which can be turned with an adjustable spanner to regulate the flow. This is called balancing a radiator.

Some lockshield valve caps need to be unscrewed before they can be removed. Others just push on.

Air vent plugs

Square headed bleed screw and nozzle One of the two top tappings is fitted with an air vent plug, which has a bleed valve, sometimes known as an air release valve, for releasing any unwanted air, or ‘bleeding’ the radiator.

They vary in appearance but most have a similar square-headed bleed screw, sometimes called the bleed pin, at their centre. The bleed screw head is usually 5mm square.

When the screw is loosened sufficiently, first air, then a little water, is released through a nozzle, before it is re-tightened.

Hexagonal radiator bleed plug If the air vent plug has an external (male) hexagon nut fitting, it can be fitted or removed with an open-ended or adjustable spanner.
Square section bleed plug Some radiators have square internal plugs, known as square sections, which can be fitted or removed with the square end of a double-ended, Allen or universal key.

Blanking plugs

Radiator blanking plug The other top tapping is fitted with a blanking plug, which simply plugs the hole that would otherwise let out water.

These can have hexagonal heads – like this one – square heads, or square section recesses.

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