Featured General

Draining a central heating system – what you need to know

There are times when any central heating system needs to be drained. These might be to fix a leak, replace a radiator or otherwise make repairs or enhancements to the system.

Water damage is one of the most common causes of household insurance claims, https://www.iii.org/fact-statistic/facts-statistics-homeowners-and-renters-insurance so if you are planning on draining your heating system yourself it’s important to know how to do it safely and properly.


Before you start you’ll need a length of hosepipe, and a wrench or pair of pliers. Locate the drain valve, this may be below the boiler or on one of the downstairs radiator connections – often systems have more than one drain point.

Image Credit

Before you start turn off the power to the boiler – this is usually located next to the programmer or the boiler itself in the form of a fused spur. Next, if you have an open vented system, turn off the water supply to feed an expansion tank in the loft. This will usually have its own isolator valve, if it hasn’t you’ll need to turn off the main water supply at the stop tap. On a combi system turn off the water supply to the boiler, again there should be an isolator.

Getting started

Now you’re ready to start, connect your hose to the drain valve and run it outside, preferably to a drain. If you’re in any doubt about draining the system yourself, a Gloucester emergency plumber such as http://www.hprservicesltd.com/emergency-plumber-gloucester/ will be able to do the job for you.

With the hosepipe connected, use your wrench to open the drain valve and the water should begin to flow out. The flow will be pretty slow at first and in order to speed it up open the radiator bleed valves. Start at the top of the system – this will be one of the upstairs radiators, the one that most often suffers from airlocks. There may also be a vent valve near the hot water cylinder if you have one. As the water drains out work your way down, opening the bleed valves on the downstairs radiators too.

Remember to close the drain valve again before refilling and use the bleed valves to control the flow. Remember too that the system will need corrosion inhibitor added when it’s refilled to prevent long-term damage.

Leave a Reply

Your email address will not be published. Required fields are marked *