Drain a radiator and remove a radiator: how-to guide

Whether you need to drain a radiator or remove a radiator, these are not difficult tasks. In fact, you won’t even need to drain the central heating system.

How to drain a radiator

Close the valves

The first thing to do is to close both radiator valves: the lockshield and the TRV (thermostatic radiator valve.

Next, turn the central heating off and allow the system to completely cool down. Don’t attempt this job until it has done so – the water inside your central heating system is extremely hot and can cause burns.

To turn off the lockshield, first remove its plastic cap. Next, use an adjustable spanner to turn the key clockwise until it won’t turn any further.

It’s really important that you remember how many times you have to turn it before it’s shut. When you’ve finished this job, knowing how far you have to open the valve will save you from having to balance the radiator.

As for the TRV, simply turn it clock clockwise until it’s closed. Depending on the valve, the close point may be a little zero or a frost symbol.

Drain the water

If you’re lucky, the radiator you’re working on may have a draincock built into one of the valves. In this case, you can simply connect a hose to the draincock, open it up, and drain the water outside.

If it doesn’t, the easiest way to drain the radiator is to partially open the nut that secures it to the lockshield, and let the water drain into a shallow plastic container, such as an old airtight food container or a paint mixing tray. You can then decant this water into a bucket.

Before you do this, you should cover the nearby skirting board and carpet with old towels. The dirty water inside the radiator can – and usually does – splash much further than you think. If it’s possible, lift the carpet up and pull it away from the radiator a good distance.

To open the valve and start draining, hold the lockshield with a pair of grips or water pump pliers, and open the nut using a pair of adjustable spanners. Some water should come out, but the majority will be stuck inside via a vacuum. Use a radiator key to open the radiator’s bleed valve, and the water should really start to flow.

Drain a radiator – disconnect the radiator

Once the water has stopped flowing and you want to remove the radiator, the next thing is to disconnect the lockshield completely.

Do the same thing for the TRV: grip the valve by its body (not its plastic cap) with a pair of grips, and open the nut with your adjustable spanner, taking care to catch any water that may come out.

Remove the radiator

Once you’ve disconnected the radiator at both sides, you should then be able to remove it. A standard radiator is usually held to its bracket by nothing more than gravity, and you should simply be able to lift it up and off. However, depending on its size, you may very well need someone to help you with this. Radiators aren’t solid but they are still made out of steel. Don’t underestimate how high you might have to lift it.

Once you’ve removed it from the wall, tip one of the outlets into your bucket to empty the last bit of water that’s still inside.

Drain a radiator – cap the TRV

Whether you are clearing sludge out of the radiator or replacing it with a new one, before you continue the rest of your job, you must cap off the TRV immediately.

Remember that the only thing keeping the TRV closed is the warmth of the room. If the temperature drops low enough, the valve may open by itself.

Most TRVs come with caps that you can simply screw onto the open end. If you don’t have one to hand, you can easily buy one from your local DIY store or plumbers’ merchant.

Refilling a radiator

Refilling the radiator is simply these instructions in reverse. Keep the bleed valve open while the radiator refills so that the air can escape,. Hold a cloth underneath the valve to catch the water when it starts to flow.

If you have a feed and expansion cistern in the loft, your central heating system should refill itself automatically.

If, after this task, several of your radiators are cold at the top, then there is a good chance that the system hasn’t refilled. You can confirm this by checking the F&E tank to see if it’s empty.

Combi boiler

If you have a combi boiler, the radiator won’t refill by itself, and the pressure in the system will probably have dropped enough to trigger a low pressure fault on the boiler. Use the filling loop to top the system up to the right pressure, which is usually 1 – 1.5 bar when cold.

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