So, what is blanking plug and why do you have to remove them to bleed a radiator? In fact, why do you have to bleed a radiator in the first place? First things first; a blanking plug (or the very similar bleed plug) is a small, elegant looking plug – either circular or hexagonal – that you usually find at the top of a radiator, on its side, so at a 90°-angle to a wall. Blanking plugs are fitted to radiators because the latter are devices whose insides require plugging at high formation pressures.

And, don’t doubt it, inside a radiator, air pressure’s a big deal. Indeed, it’s essentially for this reason that it’s crucial you bleed your radiator should you feel there’s significant air trapped inside. Too much of a build-up of excess air (i.e. trapped air bubbles) in a unit will likely result in the thing not heating up properly and remaining warm – and could even damage the radiator if nothing’s done. Now, the point to take away here is that, as so many modern radiators are fitted with blanking/ bleed plugs, should you feel you need to bleed one, you’re going to have to remove the blanking/ bleed plug to carry out the bleeding process.

Bleeding a radiator.

 


Preparation For Removing a Blanking Plugs

To remove a blanking/ bleed plug from a radiator, you’ll need a specialist key. The most appropriate would be a double-ended radiator key whose 10mm-ends are square-shaped. Having said that, if you have one lying around, an Allen key, a hex key, a universal key or a combination key/ wrench would probably also suffice.

Indeed, any of them would probably be capable of fitting into the square recess of a blanking/ bleed key and, therefore, be able to remove it from a radiator unit – yet, the advantage with a square-ended radiator key is that its end features a deliberately designed small clearance hole, so it won’t harm a bleed plug’s screw as you insert the key in the plug’s recess and turn it.

It’s worth noting too that many modern radiators feature hexagonal-shaped blanking/ bleed plugs. To remove these from a unit, you may not need a radiator key (or any of the other alternative keys mentioned above); instead, you’ll probably find an adjustable spanner or an open-ended spanner (of the appropriate size) does the job best.

 

Removing and Re-fitting Blanking Plugs

So, to remove a blanking/ bleed plug to bleed a radiator (and then re-fit the plug or fit a new plug when you’ve finished), follow the handy step-by-step guide that follows:

 

    1. First off, you need to switch off the central heating system, so you can isolate the radiator you’re going to be working on.
    2. To successfully isolate the unit (whatever type of model we’re talking about here, it’s all the same; horizontal radiators or vertical units, classic cast-iron models or heated towel rails), turn down its thermostatic radiator valve (TRV) to the lowest possible setting to make sure the valve remains closed and no hot water can flow into the unit.
    3. Next, you need to close the radiator’s Lockshield valve. Again, whatever the model (flat panel or curved bar or whatever), this valve is best turned off and back on via an adjustable spanner. Turn it anti-clockwise, all the way, to close it.
    4. It’s now time to loosen the union nut so that a little excess water can escape via the TRV or Lockshield valve; be sure to place a small container or towel underneath to catch any dripping water as the nut slackens. To loosen it, an adjustable spanner is best. You might want to quicken the water flow here by carefully loosening the bleed valve itself at the top of the radiator.
    5. Now you’ll want to re-tighten the union nut; the nut doesn’t need to be loosened for that long, though, as only a small amount of liberated water’s needed for removing a blanking/ bleed plug.
    6. Finally, we move on to removing the blanking/ bleed plug itself. To do this, use the most appropriate key you’ve identified for the task, as outlined above, or use the most appropriate spanner. Whichever implement you choose for the job, you’ll need to turn it anti-clockwise.
    7. If you’re going through this process not just to remove a blanking/ bleed plug to bleed a radiator, but also (or, in fact, only) to fit a new blanking/ bleed plug, now’s the time to replace the removed plug with a new one. To do so, use the same implement as before and, having fitted the new plug in place, turn the latter clockwise. Note: if you’re tightening a bleed plug, not a blanking plug, remember too to tighten the bleed screw in the plug’s centre.
    8. Following the (re-)fitting of the plug, re-open the Lockshield valve and replace its plastic cap.
    9. Last but not least, you can now bleed the radiator, so any excess air bubbles are totally released; obviously, you’ve partially bled the radiator already via the opening of various valves, but performing proper bleeding will remove all air that may have got into the unit.
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