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How to drain your central heating system

We’ve asked our experts to help us put together an easy-to-follow guide about how to drain your central heating system in the quickest and most efficient way possible.

Knowing how to drain a central heating system is a handy skill when your home suffers from cold spots or radiator leaks.

It can be daunting, especially when there are different methods and considerations to take into account. For example, knowing how to drain a central heating system and refill it will depend on the make and model.

Thankfully, we’re here to help. We’ve asked our experts to help us put together an easy-to-follow guide about how to drain your central heating system in the quickest and most efficient way possible.

For best results, we would always recommend you hire a professional to do the job for you.

Why drain your central heating system?

How to drain your central heating systemRegular maintenance is required every three to four years to keep your heating system running smoothly and efficiently.

Although most homeowners perform emergency drainage because of sludge or a leak, this shouldn’t be the only time you consider draining your system.

Do you need to drain your central heating to change a radiator?

In most cases, it’s necessary to drain your central heating if you want to change or remove a radiator.

You’ll also need to drain it if you want to add an inhibitor, which is a chemical solution that stops rust and corrosion from causing issues within the system. This is always a good idea if you want to increase the longevity of your heating system and enhance its performance and efficiency.

How to drain a central heating system

Although we always recommend hiring a professional to drain your heating system – mainly because they have the expertise and know-how – we understand money is sometimes tight.

However, before we teach you how to do it yourself, note that hiring a professional to drain your heating system will cost you around £80, not to mention the priceless gift of peace of mind.

When you hire a Checkatrade professional, you’re hiring vetted professionals, guaranteed by us. The reviews you see on our tradespeople’s profiles are real and double-checked by us to guarantee their legitimacy.

Read our guide: How much does a boiler service cost? for more information.

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How to drain your central heating system and refill it

How to drain your central heating blogBefore you get started, grab yourself the following items:

  • Radiator key
  • Hosepipe
  • Bucket
  • Blankets/dust rags
  • Spanner
  • Screwdriver
  • Jubilee clip/zip tie

Once you’re equipped, it’s time to get to work.

Step one: Turn off your central heating system

Turn off your boiler and let your pipes and radiators cool down before you fiddle around opening and closing any valves.

Step two: Put out any fires

For boilers that burn solid fuel to keep your home toasty, put out their flames and let the unit cool down.

Step three: Cut off the water supply

Locate the stop tap or isolation valve on your boiler and turn it to cut off the water supply. The last thing you want is water filtering through your pipes when you’re trying to drain your heating system.

For combi boilers, you’ll need to close the stop valve on your mains supply. This is often located under your sink. And for water storage cisterns, you’ll be able to find the valve on the system itself and stop it from supplying water to your boiler.

Step four: Attach the hosepipe to the drain-off valve

Now everything is turned off, it’s time to find the radiator in your house that has a drain-off valve. It’ll be at the bottom of the unit on either side and tends to lean out at a 45-degree angle.

When you find it, attach your garden hose pipe to the valve (with the other end in your garden drain hole or a bucket) and clip it with your jubilee clip or cable tie so it’s secure and doesn’t let any water escape.

Put a towel on the floor on the area beneath the radiator just in case you need to catch any runoff.

Step five: Open the bleed valves

Open every other radiator bleed valve in your house before returning to the radiator with the hosepipe and opening the drain valve. This will trigger the water to start draining out.

Top tip: Bleed your radiators before you drain your heating system to speed up the drainage process. Start at the top of your house and work your way down. Read our how to bleed a radiator blog for more information.

Step six: Re-tighten all the valves

Start by closing all the bleed valves and then finish by closing the drain-off valve. Finally, take off the hosepipe and clean up any spillage.

Step seven: Refill your system

Once you’ve closed all the valves, the last step is to refill your heating system.

To do this, simply open the isolation valve on your boiler and wait while the water fills back up. Once it reaches the required pressure, turn your boiler back on and check your radiators to make sure they’re in good working order.

They might need bleeding again to remove any air in the system. However, everything should be good to go.

Top tip: You can also add an inhibitor solution as your boiler refills to limit the build-up of sludge and limescale.

Can you drain a central heating system and still have hot water?

No, leaving the hot water on when draining your central heating isn’t recommended and can damage your system. It takes around an hour to drain your heating system, so factor in whether you can live without hot water during that period. As long as you follow the above steps, your boiler should work as normal as soon as it’s refilled.

Did you find this ‘How to drain your central heating system’ blog useful? If so, there’s more where this came from. For more expert advice, how-tos, and top tips, check out our other articles here

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