How to fit and remove blanking plugs and bleed 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.
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.
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.
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.
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.
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
Step 1 - Turn off heating system
Before removing a bleed plug, turn off your central heating system and isolate the radiator.
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.
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.
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.
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.
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.
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.
Step 8 - Re-open lockshield valve
After fitting the new plug, re-open the lockshield valve and replace the plastic valve cap.
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: