How to Drain a Radiator Safely Without Making a Mess

How to Drain a Radiator
How to Drain a Radiator

There are several reasons why you might need to drain a house radiator down to repair it or remove it. It may not be working properly because gunge has collected at the bottom and is obstructing the hot water supply. On the other hand it may be leaking and you had to turn it off to save the carpet.

Whatever the case may be, you may have to do this several times in your lifetime. We tell teach you how to it here, because we love giving away free information about our passion, central heating systems. Remember though, if you do get stuck or decide to use an expert then Worcester Bosch is just a few clicks away.


There are several steps involved in draining your radiators. By following these steps carefully, you’ll be able to bleed your radiator lines properly, and will have them back to their original working order in no time.

How Central Heating Works in UK Homes

Most UK homes are heated by warm water from a boiler flowing through pipes and radiators. These are generally-speaking trouble free, although modern radiators have their own connections just in case one gives trouble.

You’ll be glad to know you don’t have to drain the whole system down and lose all your hot water. However you should always turn the switch off at the main boiler control panel, and wait until the pipes leading to the radiator in question cool completely before attempting to drain a house radiator for replacement or repair.

Getting Ready to Drain a House Radiator without Making a Mess

While you wait for the pipes to cool double check you have the following tools and equipment ready and in good order. You will also need an assistant to help you loosen and remove the various pipes and radiator as the job proceeds.

  • Two suitable containers that fit under the radiator pipes
  • Two old hand towels you don’t mind getting dirty
  • A pen and notebook to record the lock shield setting
  • A container of some kind to keep any bits of radiator you remove
  • A medium size pair of pliers or an adjustable spanner
  • Several absorbent cloths for wiping up any mess
  • Special tool to open the bleed valve and admit air
  • A pair of stout gloves to protect your hands from harm
  • A set spanner that fits the union nuts on the radiator
  • A roll of fresh adhesive tape approximately a half inch wide
  • A plastic bucket and a bag for recycling garbage

Step One – Prepare for the Job

Locate the pipes on either end of the radiator. The one with the regulator control receives the hot water from the boiler, while the other one – the lock shield valve – sends it back again.

Fold the two hand towels separately into squares measuring a foot by a foot, and position them under the regulator and lock shield controllers. Set the two containers on top of these so at to catch water drips after you loosen off the pipes.

Step Two – Isolate the Radiator

Isolate the radiator from the heating system by closing the two valves. The regulator side is easy. Turn the setting down to zero in a clockwise direction. The lock shield one is trickier so have your pen and notebook ready.

First, remove the small white cap to get access to the valve itself, and place this in the container for safe-keeping. Now use the pliers or adjustable spanner to close the lock shield fully going clockwise. Count the number of full turns and write this in the notebook.

Step 3 – Get Ready to Drain a House Radiator Down

Inspect the set spanner carefully to make sure the faces are still square. Do not use an adjustable or shifting spanner because it could slip and damage the radiator, worse still your hands.

Check the spanner fits both union nuts tightly and imagine you are using it to loosen the unions going anti-clockwise. Are there points where your spanner hand could bump something if the spanner slipped? Wrap an old cloth around that point if you can. Use the special tool to open the bleed valve two turns.

Step 4 – Loosen the Union Nut on the Regulator Side

This can be the trickiest stage in the procedure to drain a house radiator. That’s because this is the step most likely to spill water. Check the container is still in position under the union nut, and your assistant is standing by with absorbent cloths.

Now fit the spanner to the union nut on the regulator side of the radiator. Have your assistant steady the pipe while you turn the nut slowly anti-clockwise a quarter turn until water starts to bleed out into container. Never force the spanner. If you can’t budge it you may need to find a gas safe engineer with special tools on our website.

Take your time with draining the radiator into the container. Tighten the union before it gets full, and discard the water before continuing. If the water does not flow willingly open the bleed valve a bit more to break the partial vacuum.

The water flow will finally slow, and then stop completely. If your back gets a crick or your leg start to cramp, take a break. Make a cup of tea and enjoy it in the garden if it’s summer. At this stage you may be realising that plumbers really do earn their money.

Step 5 – Remove the Couplings from the Unions Completely

Unscrew the union nut completely from the radiator on the regulator side and gently pull the supply pipe slightly away. Cover the pipe thread with the adhesive tape to protect it from any bumps and knocks.

Now remove the union nut on the lock shield side of the radiator. Work carefully because some water may still drain. Move the drain pipe gently away, and protect the pipe thread as you did at the regulator end.

Step 6 – Remove the Radiator and Drain Away the Last Water.

Place the plastic bucket on the opened-out bag for recycling garbage conveniently nearby. Kneel at one side of the radiator with your assistant at the other end. Cover the holes where you removed the pipes with one hand while you use the other one to pull the radiator upwards away for the wall bracket.

Now finally drain the last of the radiator water into the bucket until it stops dripping. Congratulations! You now know how to drain a house radiator without making a mess, and you may have even done it without a plumber.