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    How to fix: Radiators that are cold at the bottom

    If you’ve got your heating on but aren’t feeling the benefits of the heat in your home, there can be a few reasons for this. One thing to check if you know your boiler is working as it should be is the radiators. It might be that your radiators feel nice and warm on the top but ice cold on the bottom. When this happens, you’ll want to resolve the issue as soon as possible – not only so that your house will feel warm again and you can prevent wasted heat, but also to save you money on your energy bills. See how to fix radiators that are cold at the bottom in this guide. 

    First, what causes radiators to be cold at the bottom?

    The most common cause of radiators being cold at the bottom when they’re switched on is a build-up of sludge. When sludge starts to gather within the radiator and in its internal elements it causes a blockage so water can’t pass through and move round the system as it should. Due to the weight of the sludge it typically sinks to the bottom of the radiator where the entry and exit points are, hence, why it will be hot at the top and cold at the bottom. 

    Why does sludge form in radiators? 

    Radiators and their associated pipework are made from metallic components, normally either iron or steel. The persistent contact with water as it passes through the system results in natural debris forming from stagnant water and compounds like the iron oxide magnetite. As these accumulate alongside other mineral deposits like limescale they start to create the sludge and ultimately block the water flow. 

    How to fix radiators that are cold at the bottom

    A blockage in your radiators caused by sludge isn’t going to solve itself. In fact, the longer you leave it the worse the problem will become as you are giving the sludge more time to form and block more of the system. Not only that but it can eventually lead to issues with your boiler if your radiators aren’t fixed and the blockage cleared. So, if you suspect your radiators are blocked don’t ignore it, or you could end up paying out for heating replacement parts for your boiler and radiators. 

    There are a few ways to fix your radiator issue and if you’re experienced in DIY, you can probably do this yourself. If not, you’ll want to contact a heating engineer. In any case the below options will give you an insight into how the blockage can be removed and your system can be working effectively again. 

    Chemical flush 

    A chemical flush combines strong chemicals together which you can introduce to your radiator to break down the sludge blockade. Similar to when you have a blocked drain and pour chemical cleaner down it. The chemicals usually take around an hour to get through the radiator system, but it can be left there for up to week if you think it hasn’t fully rectified the issue. This type of flush is best done by a plumber or heating engineer. 

    Powerflush the radiators 

    A powerflush involves pushing highly pressurised water through the heating system and radiators. The idea behind this is that it will apply a significantly stronger force to the blockage than the normal water flow and break it down so the water can pass through. If you have more than one radiator that is cold at the bottom, then a powerflush will probably be your best option. Again, you will likely need a professional plumber for this as a powerflush can lead to a lot of mess if it isn’t done correctly. 

    Manual flush/bleed the radiators 

    Bleeding and manually flushing the radiator is the main way you can get rid of a blockage yourself and will likely be the best option if you only have one that is cold at the bottom. If you aren’t too sure how to manually flush your radiator the steps below will give you a quick overview: 

    • Make sure your heating is fully switched off and you leave enough time for the radiator to get cold. 
    • Put an old towel or sheet down underneath the radiator to protect your floor and a bowl to collect the water during the process. 
    • Use the bleeding key to open the valve at the top of the radiator so air can flow through, and water can drain out. 
    • When the water has all drained out, undo the valves, and take the radiator off its brackets. 
    • Take the radiator outside and flush it with your garden hose until clean water comes out of the other side. 
    • Bring the radiator back in and put it on its brackets, re-attaching all the necessary components. Have your bleeding key ready to close the valve when water starts to escape. 
    • If you have a pressurised system that won’t repressurise itself, you might need to use the loop and add extra water to build up more pressure to the right level. 

    Conclusion 

    Hopefully this guide has given you the information you need to be able to effectively fix your radiators when they’re cold at the bottom – whether you’re doing it yourself or using a professional plumber or engineer. If you’re having problems with your boiler or heating system and need a specific part to fix the issue, NBS can help. We provide high quality new and refurbished boiler parts at affordable prices from a wide range of brands. Find the boiler spare you need from our online shop today.