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How to fit and remove blanking plugs and bleed plugs?

How to fit and remove blanking plugs and bleed plugs

Shop for Radiator Keys

Keys for use on radiator plugs You can use the square end of a double-ended radiator key, an Allen or hex key, a universal key or a combination wrench/key to fit and remove square section blanking plugs and bleed plugs.
Square section radiator bleed plug A square section plug has a square recess into which the key’s square end fits perfectly. A clearance hole in the square section of the key ensures the key does not damage the square-headed bleed screw in the middle of the plug.
Hexagonal radiator bleed and blanking plugs Many modern radiator bleed plugs and blanking plugs are shaped like hexagons. You do not need a radiator key to fit and remove these – you can use an open-ended spanner of the right size, or an adjustable spanner.
Radiator bleed plug with square recess However, some bleed plugs and blanking plugs have a square recess which the 10mm square end of the key fits into.

This is a bleed plug with a 10mm square recess. The blanking plug is similar but does not have the square-headed bleed screw in the middle.

Panel radiator If not already fitted, bleed plugs and blanking plugs need to be fitted to radiators when a new system is being installed. On existing systems, reasons for replacement might be corrosion or leakage, or both.
Damaged radiator bleed screws Other reasons include the bleed screw in a bleed plug seizing up or the square bleed screw’s corners becoming worn and rounded. In such cases, it may be impossible to loosen the bleed screw.

Depending on your type of bleed plug, you may be able to get new bleed screws rather than replacing the whole plug.

Removing and fitting bleed and blanking plugs

Turning off the heating system

Step 1 – Turn off heating system

Before removing a bleed plug, turn off your central heating system and isolate the radiator.

Turning off thermostatic radiator valve

Step 2 – Isolate radiator

To isolate the radiator, turn the thermostatic radiator valve (TRV) at the bottom left or right to its lowest setting. This will ensure the valve stays closed.

Lockshield valve with drain

Step 3 – Turn off the lockshield valve

Remove the plastic cap from the lockshield valve on the other side and, using an adjustable spanner, turn the valve anti-clockwise until it is completely closed.

Undoing radiator valve union

Step 4 – Loosen union nut

Place a container under the TRV or lockshield valve to catch the water and loosen the union nut – the large nut that connects the valve to the radiator tail – with an adjustable spanner.

Once the union nut is slackened, water may start to drip from the joint. You can speed up the flow of water by loosening the bleed valve on the top left or top right of the radiator.

Re-tightening radiator union nut

Step 5 – Re-tighten union nut

Remember, you only need to drain a little water from the radiator for the purpose of removing a bleed plug or blanking plug.

To stop the water draining, re-tighten the valve’s union nut.

Removing-fitting square section radiator plug

Step 6 – Remove the plug

To remove the bleed plug or blanking plug, insert the square end of your key into the square recess.

There is a hole in the middle of the end of the key which ensures the key does not make contact with the square-ended bleed screw in the middle of a bleed plug.

Gripping the handle of your key, turn it anti-clockwise to remove the plug.

Square end of double-ended radiator key

Step 7 – Fit replacement plug

You can now fit a replacement plug, again using the square end of the double-ended key. If you are fitting a bleed plug as opposed to a blanking plug, make sure the bleed screw is tightened as well, using a bleed key.

Replace lockshield valve cap

Step 8 – Re-open lockshield valve

After fitting the new plug, re-open the lockshield valve and replace the plastic valve cap.

Bleeding a heating radiator

Step 9 – Bleed radiator

Now bleed the radiator to remove the air that got in when it was partially drained.

For a step-by-step-guide to bleeding radiators, see: How to bleed a radiator

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