How to Drain Down a Central Heating System

Large tap on plumbing pipes

Draining down a central heating system may seem like a large and imposing task. However, if you arm yourself with the right advice and equipment, then you may find that the job is easier than you ever thought.

To help you decide whether you have the ability to drain down a central heating system yourself or whether you need the help of a professional, we’ve put together this guide that contains everything you need to know.

How often should you drain your central heating?

In order to function effectively and efficiently, your central heating system will need draining from time to time. After all, by draining down your central heating system fully every now and then, you can remove sludge from the system, repair any leaks or change a radiator.

Draining down a heating system isn’t something that needs doing with great regularity. However, that said, we recommend that you drain down your central heating system every five years or so. Of course, if you spot a leak, you should drain your central heating system as soon as possible to repair it and prevent any damage.

Step-by-step guide to draining down your central heating system

Step 1: Get your tools

Before you begin to carry out any work on your central heating system, you should gather all the tools you need. To drain down a central heating system, you will need:

  • An adjustable spanner
  • A flathead screwdriver
  • A hose pipe
  • A jubilee clip
  • A towel
  • A radiator key

Step 2: Switch off the heating

Before you start, you’ll need to make sure that your entire central heating system is switched off. This way, you can work safely. If your system has recently been switched on, wait until the system and your radiators cool.

If you have a conventional heating system, then you should also isolate the water going into your system’s header tank before you switch off your boiler. Similarly, if your boiler has a water intake valve, you should also close it off. This will ensure that no water enters the system while you’re working.

Step 3: Connect your hosepipe

When everything is off and cool, connect your hose pipe to your radiator’s drain-off valve. This should be located on a radiator that’s downstairs in your home.

When it’s attached, tighten it with the jubilee clip to ensure water doesn’t leak. To make sure nothing is damaged, place your towel on the floor under the valve. If required, you can tighten the jubilee clip using a flathead screwdriver.

Once you’re happy this end is secure, place the other end of the hose outside; preferably near a drain.

Step 4: Open the drain valve

Once you’re happy that the hose is in a position to effectively drain the water, open the valves on the radiators in your home. Once the valves on the other radiators are open, return to the radiator where the hose is attached and open up the drain-off valve. Water will then start to drain.

Step 5: Open the bleed valves

When the drain-off valve is open, you can open the bleed valves on your radiators. Start on the radiators that are upstairs in your home and open them by turning them anticlockwise with the bleed key. If you’ve done this correctly, you’ll hear a sucking noise. This noise is absolutely nothing to worry about, it’s just the noise of air entering the radiator.

Once you’ve opened all the bleed valves on the upstairs radiators, check water is coming out of the hose pipe. If it is, wait 10 minutes and then carry out the same procedure for the downstairs radiators. However, if you open a bleed valve on a downstairs radiator and water starts to come out, quickly retighten it and wait 10 minutes before trying again.

Once all the bleed valves are open and the hosepipe has stopped draining, you can carry out any work. Before you start though, it’s best to close the valves back up again. At this point, you can also remove the hose and close the drain-off valve.

Can you use hot water when your central heating is drained?

Depending on the work you’re carrying out, your system may be switched off for a lengthy period of time. As a result, if you have a combi boiler, you may want to take steps to ensure you can still use hot water while the system is drained down.

To do this, you’ll need to cap the pipes and isolate the boiler from the system. Then, you’ll need to pressurise the boiler to 1.5 bar and switch your boiler back on. However, when you fill the system back up you’ll need to add an inhibitor and bleed all the radiators. Before you do this though, you should consult an expert.

Although draining a central heating system is straightforward if you follow the steps outlined above, you should still seek professional advice about whether this method is right for your heating system before you begin any work. For example, if you don’t have a drain valve on your central heating system, you may need to fit a drain point to the top of the radiator or remove a radiator entirely to drain the system. This will likely require the help of an expert.

That said, draining down your central heating system is a great way of carrying out maintenance. If you’re thinking about draining down your heating system so you can install a new radiator, take a look at our selection today to find the perfect replacement. Or, contact us for support.


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