How to Drain a Central Heating System

how to drain a central heating system

A central heating system is a crucial element in every house. It heats up your property and provides you with hot water.

It goes without saying that you should do whatever you can to keep it up and running. One of the good maintenance practices is the draining of your heating system.

But why exactly should you drain your central heating system?

You should do it every once in a while for a number of reasons. Draining central heating helps remove the build-up of sludge and limescale, which is important to its overall maintenance.

It’s also a necessary step when you’re about to add an inhibitor to the system, remove a radiator, or fit a new one. Additionally, you must drain the whole central heating system before you do any heating or boiler repair works.

Regardless of your reason, you probably don’t know how to do it if you’re not an expert.

Don’t worry! In this article, you’ll learn how to drain a central heating system with and without a drain valve.

Here’s everything you need to do to proceed:

How to Drain a Central Heating System

If you want to drain your heating system, follow these steps:

  1. Turn off your system and wait until the pipes and radiators cool down.

  2. Put out the solid fuel fire.

    Some boilers operate with solid fuel, so you need to extinguish the fire first and wait until the unit cools down.

  3. Cut the water supply to your unit.

    This will prevent the water from entering your central heating system while you work on it.

    To stop the water supply, tie up the ball valve to a piece of wood laid on top of the cistern. You can also use a separate stop tap if your system has one.

    If you have a sealed central heating system, you need to isolate the water flow to the water tank before switching off your boiler. On the other hand, if you have a combi boiler, switch it off, wait until it cools down, and start the draining process.

  4. Look for the right radiator and drain-off valve.

    The drain valve should be located at the bottom of the radiator.

    Once you find them, get a garden hose and attach it with a clip to the outlet. This will allow the water to run outside.

    You can also tighten the clip with a flat-head screwdriver to prevent the hose from slipping off and spilling water everywhere. Just remember to put the hose away from your plants and lawn because there may be harmful chemicals in the inhibitor.

    In case you have no hosepipe, use a bucket and shut off the valve each time you empty it.

  5. Bleed your radiators.

    This way, you’ll get rid of the excess air that prevents the water from running. If you have a two-story house, open the bleed valve upstairs and wait for about 15 minutes, then proceed with opening the remaining bleed valves downstairs.

  6. Open the drain valve and get rid of the water.

    First, double-check whether all the radiator valves in your house are open.

    Then, drain your central heating system by opening the radiator valve with the hosepipe still attached. Depending on the type of system you have, it should take you between 20 minutes to an hour.

  7. Refill your central heating system.

    First, close the drain cock on the radiator and all the valves you’ve opened.

    Unit the string in the feed tank and let the water fill up the device. Bleed the radiators downstairs when the tank is full. Then, go upstairs and repeat the process.

    If you managed to perform all the steps correctly, your central heating system should now be filled.

Pro tip: If you want to limit corrosion and limescale build-ups, add an inhibitor to your central heating system.

How to Drain a Central Heating System Without a Drain Valve

Some systems don’t have a drain valve. In this case, do the following:

  1. Shut down your central heating system and cut the water supply.

    Wait for the pipes and radiators to cool down completely before you move on to the next step. If you have a conventional system, isolate the water first and then turn off the boiler.

    With a combi-boiler, you need to turn it off, wait for it to cool down, and then discharge the water.

  2. Separate the radiator from your central heating system.

    Do it by closing the two valves and rotating the regulator in a clockwise direction. Then, remove the plastic cap from the lockshield, grab the pliers and close the valve back tightly.

  3. Bleed your radiators.

    To speed up this process, open up all bleed valves and release excess air. Don’t forget about a bucket or a towel to prevent the floor from becoming wet.

  4. Loosen the union nuts and stop the leaking water.

    First, you should release the coupling nut on the regulator side and put a towel or a bucket underneath to dry any leaking water quickly. Rotate the nut counterclockwise with a spanner until the water starts pouring into the bucket. 

  5. Drain your system with a hose.

    Attach it to the radiator valve when it’s still separated from the system. Use a special fitting to attach the hose – speed fit draining fitting or a speed fit tap will do.

  6. When you manage to drain the radiator completely, take it off the wall to avoid water staining.

    Make sure to drain it from both sides.

  7. Complete the process by closing off the valves and removing the hose.

The Bottom Line

Every once in a while, you should drain a central heating system in your home. While it’s not the most straightforward process, you can certainly do it on your own. Remember that good upkeep of your central heating system will ensure its efficient performance and help you avoid costly repairs.

Feel free to use this article as a checklist next time you have to drain your system. If you follow all the steps, you should complete the process without much hassle.

However, if you feel lost at any stage, reach out to an expert and have them do it for you.

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