How to Drain a Central Heating System

Written by  John Davies
Last updated: July 5, 2023

There have been many innovations in home heating and water heating systems. However, most homes still use a good old-fashioned boiler to provide both. These systems work by circulating hot water or steam throughout the house via a system of pipes and radiators.

To make the most of this system and prevent unnecessary problems, you will find it necessary to drain the central heating system on occasion to solve problems such as removing sludge and repairing a leak. You will also need to perform this process to change the radiator.

Is Draining a Central Heating System a DIY Job?

Yes. It is a reasonably easy job to execute your own with little risk to the heating system or your property. However, if something goes wrong, do not think twice and call a professional plumber immediately. Do not try to reverse the damage yourself. Instead, focus on containing any leaks or secondary damage.

What Do I Need to Drain My Central Heating System?

It is a relatively simple job that does not require too many tools:

  • A hosepipe
  • A bleed key
  • A pair of grips
  • An adjustable spanner
  • A jubilee clip
  • Rags or towels

Step-by-Step: How to Drain a Central Heating System?

Step 1 – Turn off the boiler

Turn off the boiler and/or the central heating system. In many cases, you can turn this off at the mains water stopcock. In others, you may need to find the isolation to the central heating tank or the gate valve located after the main heating tank.

Remember, in a combination boiler. You do not need to turn any radiator valves off before you get started. Then wait an hour before proceeding. This is an essential safety measure. That way, the dangerously hot water inside has a chance to cool off to a more moderate temperature.

Turning off the boiler will also lower the distress on the system and reduce the chances of a malfunction.

Step 2 – Shut off water intake valve

Shut off the water intake valve. To complete the safety measure of turning off the boiler, you will also want to prevent the entry of hot water into the system while you work. Therefore, it is vital to address the intake valve.

Step 3 – Use a bucket (or hosepipe) to control drain off valve

Use a bucket or hosepipe to control runoff from the drain-off valve. There are usually located indoors, and therefore, you will need to take extra measures to prevent fluids from accumulating within the premises. You will also want to place a towel underneath the spot, as fluid can leak despite the precautions.

Locate the drain-off valve, which is not always in the most obvious location. It is better to use a hosepipe than a bucket in this situation because the bucket may run over in some cases.

However, make sure that the hosepipe is long enough to reach outside the hose, to a location where leaks will not cause any undue damage. It is not advisable to allow the water to run into your flowerbeds since the drained fluid contains heating chemicals that are unhealthy for organic life forms. The hosepipe should fit nicely on the valve.

However, if it doesn’t, you should secure it with a jubilee clip. Otherwise, you may find that the hosepipe has slipped, and dirty water will spill all over the floor. If the hosepipe is long enough, place the end of it outside the house in a secure location. If not, place the end into a bucket or a large container suitable for fluids.

Step 4 – Drain the radiators

Drain the radiators. Use a good adjustable spanner to open it. Apply a reasonable amount of pressure and turn the valve in a counter-clockwise direction. Make sure that all of the radiator valves are open.

At this point, keep a very close eye on the drain off valves since water will begin to flow into them. If you are using a bucket, keep an eye on it during the process. You may have to empty it more than once.

Step 5 – Open bleed valves

Open the bleed valves using the bleed key. Turn the key anti-clockwise. It is always advisable to start on the top floor of the house and then work your way down. If the process is under control, open the drain valves to speed up the process of drainage.

At this point, you should hear the highly distinctive sound of the air being sucked into the system. Do not be alarmed; that means it is working! The air is supposed to go into the radiator, as it is no longer sealed hermetically.

Step 6 – Check water is flowing

Go down to the hosepipe and make sure water is flowing out of it. If the process is working, there should be at least some fluid coming out of the system. Do the same thing for the radiators, and make sure not to miss any.

Step 7 – Wait for the water to drain out

Wait patiently for 10 minutes for each outlet to empty. Allow time to pass until you are satisfied that all the liquid has been sucked out of the system. While you wait, keep an eye on the buckets, containers, and hosepipes under the radiators and beneath the drain-off valve. After the 10 minutes are up, you should find that water is no longer dripping out.

However, if there is still a flow after 10 minutes, you may have individually piped radiators. If so, drain each one of the radiators separately. The best way to do so is by utilizing the radiator drain valves. After this process is completed, you can carry out any remaining work and finish the draining job.

Step 8 – Close the bleed valves

Close the bleed pipes back up. After that, close the drain-off valve. Please do not remove the hosepipe until it is fully turned off. Next, remove the hosepipe but take care of it. Move it outside swiftly since it likely still contains some liquid.

central heating drain valve

What Else Do I Need to Know about Draining My Central Heating System?

Every unit is a bit different and has different valves and draining points. Get to know your system as well as you can before you proceed. You also may want to apply some chemicals while you are cleaning out your system. Some of them will help increase the longevity of your system and help keep it running for many years.

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