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Poor performing radiators – a troubleshooting guide

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Poor performing radiators – a troubleshooting guide

If your house simply isn’t keeping as warm as it should be, it’s worth checking that all your radiators are generating the right amount of heat. If you find one that isn’t, there can be a number of causes – some of which can easily be fixed yourself, some of which take a bit more effort – and some of which take the intervention of an expert. 

1. Trapped air in the radiator

 Let’s start with the easiest (and the most common) one. If your radiator is hot at the bottom but cold at the top, then it’s most likely that you’ve got trapped air in the radiator. The heat for your radiator is provided by hot water which can flow freely around your system. But air is a much poorer conductor of heat, so if you get air in the radiator, only the bit that has water in it will be hot.

To remove the air, you need to ‘bleed’ the radiator. You will need a bleed key that fits your radiator (if you don’t have one, these are cheap to get from any DIY store). The radiator bleed valve will be on one side at the top of the radiator. You give it a half turn with the bleed key until you hear the sound of hissing. That’s the air escaping from the radiator. Wait for a few seconds until the hissing stops and water begins to come through the valve. At which point close it again. 

You should now, when you feel the top of your radiator, feel the heat has returned.

2. Sludge in the system

 It’s as unpleasant as it sounds! If you have more heat at the top of the radiator than you have at the bottom, then it may well be because of a build-up of sludge in the radiator. Sludge is caused by internal corrosion of pipes in the system. This collects at the bottom, making a barrier for the hot water.

Radiator sludge can result in knock-on problems in the system. The obstruction makes it harder for water to circulate, and that can create pressure that damages your boiler. So it needs to be fixed if it happens. 

This is more effort to deal with. If you’re not a confident DIYer you might want to call for professional help at this point! But if you’re happy to dive in, and the problem seems isolated to one radiator, you will need to remove the radiator from the wall and the plumbing and rinse out the sludge.

If the problem can be seen in more than just one radiator, then you probably have a system-wide sludge problem. At that point, you really have little choice but to get in a heating engineer to properly powerflush the system.

3. Balancing the system

 If radiators seem to heat up evenly, but they’re not all working as efficiently, then it may not be a problem with your radiator – it may just mean you need to balance the system. This is a process of methodically checking the degree to which the lockshield valve on the radiator needs to be opened for it to perform optimally. Radiators closest to the boiler will need the least open valves. Those furthest away the most. Any good heating engineer should do this for you after carrying out any work on your heating system.

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