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Keeping your radiator healthy

How to bleed a radiator and protect against cracking

Keeping your home snug in winter is easy when you know how. Find out how you can keep your radiators in good condition all year around – and the simple fixes you can try yourself when they need some TLC. 

 Bleeding a radiator 2

Why would it need bleeding?

If you find your radiator is warmer at the bottom than the top, or if one radiator doesn’t heat up but others do, then it might need bleeding.

The cold water is heated by your boiler gets pumped around the pipes and flows though the radiators.

But during the heating process air is released – and sometimes pockets of this air get trapped in the radiator, filling the space that should have hot water, causing to cold spots.

Bleeding, also called venting, is how you get trapped air out. So all you need to do is open the radiator’s air vent. This then lets hot water flow and your radiator can heat up properly again.

Bleeding a hot water radiator

This is a simple fix you can usually do yourself with the right tools. Most types of hot water radiator can be bled with a radiator key or flat screwdriver. You can buy a radiator key from any DIY or hardware shop, if you haven’t got one.

Then you need to either switch off the central heating or turn down the thermostat, so that the radiator’s cool enough to handle.

You’ll find the radiator valve near the top of the radiator. Before you start, have a small bucket and cloth ready to catch the water handy. You can hold the cloth under the valve to catch any drips.

Attach the radiator key into the square section at the centre of the valve, and slowly turn it anti-clockwise to open the valve. You should hear a hissing sound as air is escaping.

As soon as the air stops sputtering, water might begin to leak from the valve – this means you’re done. Close the valve quickly by turning the radiator key again, this time clockwise.

Once you’re finished, it’s a good idea to check the boiler’s pressure gauge because bleeding a radiator often lowers the pressure in the boiler. Restoring boiler pressure can be a little more complicated. You can find out how to do this in your boiler manual – it usually means turning a couple of valves, but if it requires tools, it’s probably a good idea to call a professional.

Steam radiators are different to hot water radiators, and normally bleed themselves automatically through the air vent about halfway down the side. However, sometimes the vents are painted over which means the air can’t escape. In this case, all you need to do is use a small wire or sewing needle to clear the air hole at the top of the vent and let the radiator bleed itself.

Protecting against cracking

Radiators are strong, reliable, and durable, but they do occasionally crack in particularly cold weather – this is because water expands when it freezes. You might notice some visible cracks on the radiator – these are usually at weld points and seams. You might also see rust or leak stains at the cracks.

With the hot air or water escaping, the radiator won’t be as effective, not to mention the potential dangers if there’s a burst.

Here are two ways to avoid this:

Thermostatic radiator valve (TRVs) – as the room temperature approaches 0°C, the valve opens a little to allow some hot water into the radiator, so it doesn’t freeze. Learn more about TRVs in our boiler handbook.
Frost thermostat – this will automatically turn on the central heating when the temperature drops below a set level, overriding the normal central heating timer. 

Depending on how extensive the damage is, you might need to replace the entire radiator. However, if there’s only minor damage, it may be repairable. 

Everyone wants to keep energy bills down, but if your radiators aren’t working properly or are damaged, it’ll cost a lot more to heat your home. Sometimes a quick DIY job can solve the problem, however an annual boiler service and boiler cover can help protect your central heating system from more serious issues.


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