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How to drain down a pressurised system

A quick guide to draining central heating

Sometimes – though not very often – you may have to drain your central heating system to make necessary repairs.

Watch this video guide or follow the simple steps below for full instructions on how to drain down a pressurised heating system.

What tools will I need?

You will need –

Drain Down_1_Tolls

Step 1 – Switch the heating off

Before you start you’ll need to ensure your heating system is turned off.

Man switching off a central heating system at the mains

Step 2 – Connect the hosepipe

Next, connect the hosepipe to the drain valve on the radiator, tighten up with the jubilee clip, and place a towel underneath to catch any drips.

Man attaching a hosepipe to an angled drain off valve on a radiator

Step 3 – Put the hose outside

Once you’ve done this, place the end of the hosepipe in a drain outside.

A plumber placing a hosepipe outside the front of a house and garden

Step 4 – Open up the drain valve

Using the adjustable spanner open the drain valve anti-clockwise.

Plumber using a spanner to turn the valve and drain water from a radiator

Step 5 – Open the bleed valves

Now you’re ready to open the air vents.

It’s important to start upstairs first, using the bleed key open the air vents anti-clockwise, you should hear a sucking noise – this is the air entering the radiator.

A man opening the air vent to a radiator with a radiator bleed key

Step 6 – Check on your hosepipe

After all the air vents upstairs are open check the hosepipe outside and make sure there’s water coming out of it.

Leave for 10 minutes, and carry out the same procedure for the radiators downstairs.

Water being drained from a hosepipe into the street

If after 10 minutes water still comes out the air vents downstairs, this is maybe because the radiators are individually piped from upstairs, if this is the case you’ll need to drain down the radiators individually using the radiator drain valves. Once the hosepipe has stopped draining you’ll then be ready to carry out any work.

If you’ve got any burning questions or need advice from the experts, be sure to send in your questions. We may feature them in our next blog post, too. Questions can be sent via the comments section below, Facebook or Twitter.

Please note: Our ‘How-To’ manuals are intended only as a guide to assist you with common home heating tasks. Please do not attempt to undertake this task if any of the instructions are unclear, or if you are in any doubt about what to do. Instead, seek advice from a professional.

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