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How to bleed a radiator: a step-by-step-guide for buy-to-let landlords

3-minute read

Josh Hall

3 November 2016

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Bleeding radiators might seem like a boring task, but it’s one of the best ways to improve energy efficiency and warmth in your properties.

Often, if tenants complain that the heating isn’t working properly, simply bleeding the radiators will solve the problem. The process lets out air or gas trapped in individual radiators that has built up over time, thus ensuring that the entire radiator gets warm.

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Do I need to bleed a radiator?

If you have gas central heating but the heating system is not keeping the property warm, you may need to bleed one or more radiators. This is because, in gas systems, air bubbles sometimes become trapped in the radiator, preventing heat from circulating properly around the device. Bleeding the radiator helps to get rid of these bubbles.

Often, if tenants complain about damp or mould, simply bleeding the radiators may be a quick and effective fix.

However, there may be other reasons why the heating isn’t working as it should, and you should check these before you start. Primarily, you should make sure that the boiler pilot light is on, and that the boiler isn’t leaking. On the subject of leaks, you should also check for rust or drips on the underside of each radiator, as these can be signs that the radiator itself is leaking.

Once you’ve completed these steps, you can move on to the bleeding process.

Choosing radiator keys for bleeding

First, you’ll need to gather some equipment. Most radiators require a bleeding key, which generally come with the unit. However, if you don’t know where yours is, you should be able to get one at any good DIY store. Sometimes, in lieu of a bleeding key, DIYers use small, straight pliers. However, this should be avoided where possible as they can cause damage to the valves. Some older radiators may require other tools, which are explained below.

So how do you bleed your radiators? Read on to find out in our step-by-step guide.

1. Turn on the heating

The first step is to turn on your heating system. Make sure that all of your radiators are on and fully heated before you move onto step two, in order to ensure that the pressure in the system is as high as it can be.

2. Check individual radiators

As soon as you’re up to temperature, have a check of each of your individual radiators.

So what are you looking for? Heating should be uniform across the radiator – the entire panel should be hot. However, sometimes you will notice cool spots, particularly at the top of the radiators. This indicates that it needs bleeding.

It goes without saying that the radiators are going to be hot to the touch, so take suitable precautions to make sure you don’t burn yourself.

3. Get bleeding!

Once you’ve identified the cool spots, turn the heating system back off again. Do not bleed radiators with the heating on.

To begin the bleeding process, you’ll need either the radiator key discussed above, a flat screwdriver, or a 12 point socket set, depending on your radiator. All of these are available from DIY stores. Simply insert the key or driver into the valve, which you will find at one end of the radiator, either at the top or bottom of the unit. Place a container or cloth under the valve to catch excess water, then turn the valve anti-clockwise. You may hear a hiss of gas, and then water will be expelled. Bear in mind that this can come out at quite a gush, so make sure you have a suitable container to catch it.

4. Bleeding a radiator with combi boilers

If your heating system uses a combi boiler, or another boiler that requires topping up manually, bleeding a radiator may reduce the overall pressure in your heating system, meaning that you need to top up your boiler once you’ve finished. Check the gauge on your boiler to find out, then use the filling loop to top up if necessary (this is often a handle on the bottom of the boiler).

5. If you have steam radiators

While most properties now have hot water radiators, some have steam systems. In these radiators, you’ll find an airvent midway down one side. These vents sometimes need cleaning, especially as they are often painted over during decoration. Simply clear the passage to the hole with a pin or needle to ensure that the vent is operating properly.

Changing a radiator bleed valve

If you’re unlucky, particularly if previous tenants have tried to bleed the radiators themselves without the right tool, you may find that the bleed valve itself is damaged or even sheared off.

First, you can find spare radiator bleed valves on eBay or in specialist plumbing merchant. Once they’ve been delivered, turn the valve all the way off. You’ll then see a larger ‘boss’ at its base, which you can unscrew. At this point, you’re likely to see some drips, which may be inky in colour. Make sure that you have something to catch them, and ensure that any carpet or floorboards underneath are properly protected.

Once you’ve removed the boss, simply screw the new one onto the fitting. You can then re-open the valve as you wish.

How else can I improve the heating?

As well as bleeding your radiators, there are some other simple steps you can take to improve the efficiency of the heating systems in your properties. First, you should ensure that boilers are serviced regularly – at least annually. You should also install thermostats if you don’t already have them, and set a reasonable maximum temperature.

If you’re ready to take on a slightly bigger task, you should also ensure that your properties are properly insulated. While loft insulation is clearly quite an undertaking, you can make significant but very cheap improvements simply by ensuring that windows and doors are properly draft-proofed.

So now you know how to bleed a radiator, as well as some simple tips to improve heating. Soon both you and your tenants will enjoy warmer, more energy efficient homes.

What steps are you taking to keep your property in good condition this winter? Tell us in the comments.

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We create this content for general information purposes and it should not be taken as advice. Always take professional advice. Read our full disclaimer

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