Your boiler is the beating heart of your home’s central heating setup. But no matter how hard it’s working, you won’t feel it if your radiators aren’t in tip-top shape. Radiators are fairly low-maintenance appliances. Still, they need a little care and attention every now and then to make sure they’re at their best. When we neglect them, it’s common for them to take longer to heat up, get less hot where they used to, and develop cold patches (even when they’ve been running for a long time).

If you’ve ever wondered “why is my radiator cold at the bottom?” or what it means for your home’s central heating, fear not. Cold patches aren’t a sign that your boiler is about to give up the ghost. It just means that your radiators need some TLC to ensure that they heat up efficiently.

cold radiator

 

These warm summer months are the perfect time to ensure that your radiators are ready to perform at their best when winter comes around. Let’s face it, the cold weather will be here before we know it. In this post, we’ll look at some of the reasons why your radiator may be cold at the bottom, what it means and how you can fix the problem…

What not to do

When many of us notice cold patches on our radiators, a common solution is to crank up the thermostat. But this will never address the cause of cold patches on your radiators. All it will do is drive up your heating bill. And if your boiler is working harder to heat some radiators than others, you’re likely not getting great energy efficiency anyway. 

Returning balance to your radiators is relatively easy. But in order to fix the problem, it’s important to first understand it. Let’s take a look at the most likely reason why your radiator is cold at the bottom…

 

Why your radiator is hot at the top and cold at the bottom

Unfortunately, the most common culprit is not a pretty one. To put it plainly… the problem is sludge! That’s right. Your radiators are most likely full of sludge. And when sludge accumulates within a radiator’s internal workings, it can prevent water from moving through them properly. Hence, you get the aforementioned cold patches. Because the weight of the sludge causes it to sink, that’s why it tends to settle at the bottom and the middle where the water entry and exit points are situated. There are many reasons why your radiators may stop working, but this is the most common reason why your radiators are colder at the bottom than the top.

Where does radiator sludge come from?

Nobody likes to think of their homes getting full of yucky sludge. Unfortunately, however, the materials from which most homes’ pipes and radiators are made from make sludge and blockage inevitable if you don’t take active steps to prevent them (more on that later). 

Radiators are made with either iron or steel. As water passes through them every day, iron compounds like magnetite and haematite are formed. As well as these iron oxides, limescale and other mineral deposits from your water itself can accumulate in your radiators. As these deposits accumulate, they can gather more and more matter until a blockage is created within the radiator’s flow channels. 

The water pressure within the radiator is insufficient to clear this blockage, and as such it can amass slowly and incrementally over time, eventually blocking more and more channels. As such, this can prevent the whole bottom part of the radiator from getting access to any hot water. While you may experience some slight warmth at the bottom of your radiator, this is likely residual heat conducted by the metal itself (and, to a lesser extent, the sludge) rather than any hot water. 

It’s time to take action and prevent radiator sludge from robbing your home’s heating of its efficiency.

 

How to fix radiators that are cold at the bottom

Unfortunately, the sludgy mineral deposits that make radiators go cold at the bottom are unlikely to be rectified on their own. Indeed, the longer you leave the problem unattended, the more of an issue you’re likely to have as sludgy deposits continue to accumulate. Furthermore, over time, sludgy deposits in your radiators can start to make trouble for your boiler. 

The good news, however, is that there are a number of ways in which you can clear out the yucky stuff and get your radiators back to their former efficiency. If you’re a confident DIYer, you may not even need to call out a plumber or heating engineer. Let’s take a look at some of the ways in which you can clear the sludge out of your radiators…

Manual flush

A manual flush or bleed can be carried out without the aid of a plumber. Indeed if only one of your radiators is affected, this may be the only solution necessary to restore energy efficiency to your home. Here’s how you do it;

  1. The first step is to isolate the radiator. Turn your thermostatic radiator valve (if you have one) down to zero, and close the lockshield valve at the other end with a spanner. This will most likely be covered with a plastic cap. You’ll likely only need to between a quarter and half a turn to close the valve and you should open it by this much later. 
  2. To prevent water spillage, place an old towel, clothes or rags down beneath the connector nuts. You’ll also want to place a large bowl on the towel to collect the water.
  3. Turn the radiator nuts slightly. A little black water may drip out. Don’t worry, this is perfectly normal.
  4. Open up the bleed valve at the top of the radiator, using a bleed key. This will allow air to start flowing through the radiator and water will begin to pour from near the newly loosened nuts. Your bowl will likely fill up quickly, so it’s a good idea to have more than one bowl or bucket to hand. 
  5. Once the water has fully drained, undo the valves fully and remove the radiator from its brackets.
  6. Take the radiator outdoors and attach a garden hose to one end. Flush the radiator out with the hose until the water comes out clean on the other side. For extra peace of mind, you can try the hose in different openings.
  7. Bring the radiator back inside and place it back on its brackets. Next, re-attach the pipes at the nuts and return both valves to their previous positions. Water will start to fill the radiator straight away, so you’ll need to have your bleed key ready to close the bleed valve as soon as you start to see water escape from it.
  8. Conventional feed and expansion systems will re-pressurise themselves. However, if you have a pressurised system, you may need to add more water to the loop to build up the necessary pressure.

Power flush

A powerflush works on the exact same principles as a manual flush. However, the radiator is not removed or taken outdoors. Instead, specialist equipment is used to move pressurised water through the system. As you can probably imagine, this can result in a great deal of mess if not done properly. Which is why a power flush is best left to a professional plumber. A power flush is the best option if you have several radiators that are cold on the bottom. 

radiator sludge before and after

Chemical flush

Finally, you may find that introducing a chemical cleaning agent to your radiator rectifies the problem just like pouring a chemical cleaner down your drain. In most cases, the cleaning agent works its way through the system in about an hour, although it can be left in the system for up to a week. Again, this is best done by a heating engineer or plumber. 

Preventing your radiators from getting cold at the bottom

As the old saying goes, an ounce of prevention is worth a pound of cure. And while we might use the metric system nowadays, that’s still pretty sound advice. 

Here are some ways in which you can prevent the buildup of sludge in future;

Scale reducer

Scale reducer is an agent that can be added to your water to reduce limescale which may exacerbate the buildup of sludge. A great solution for homes in hard water areas.

Add a central heating inhibitor to your water 

A central heating inhibitor is another chemical which can be added to your system to prevent the buildup of limescale and sludge by coating the system, and keeping water running through smoothly.

Install a magnetic filter

Finally, a magnetic filter can be installed in any central heating system. As the name suggests, it attracts rust, sludge and other metallic debris before it can start to accumulate in your radiators and cause problems with your heating.

When you know how to rid your radiators of sludge and prevent future buildups, you can say goodbye to cold spots in your radiators forever.

 


 

We hope this guide has helped you with your heating. If you’re interested in pursuing a career as a heating engineer, you can find out further information here. We also have a range of plumbing courses aimed at both experienced engineers and new entrants.