Why is My Radiator Cold at the Bottom & How Do I Fix It?

11th October 2022

A radiator that’s hot on top but cold at the bottom may go unnoticed for a while. After all, how many times do you check the radiator is on by touching the bottom of it? If you do find the radiator cold at the bottom, it’s important to find out why, as this could be a sign there are issues with your heating system.

Radiators should pretty much feel the same temperature across their surface. If you discover this isn’t the case, the radiator can’t efficiently heat your home and will need more energy to do the same job as one that’s working properly. This could ultimately mean higher energy bills.

If your radiator is cold at the bottom and you’re unsure what to do next, we’ve got you covered. Find out the reasons why the temperature could be uneven, how to fix the problem, and how to stop it from happening again.

Why is Your Radiator Hot at the Top but Cold at the Bottom?

Radiator not heating up evenly? One of the main causes for a radiator being hot at the top but cold at the bottom is a build-up of sludge. Over time, particles can accumulate within the radiator system, settling at the bottom of it. With enough buildup, this can significantly restrict the flow of water. When this happens, the bottom of the radiator – where the sludge has built up – will remain cold, while the rest of it heats up as normal.

If you encounter a radiator that’s hot at the bottom and cold on the top, this is more likely to be caused by air trapped in the top. This can be easily fixed by bleeding the radiator, releasing the trapped air and allowing the water to flow through it normally. Find out more on this topic through our guide on how to bleed your radiator.

If you find some radiators in your home are heating up faster than others, this can be caused by improper distribution of hot water from your boiler. Discover how to fix this issue in our step-by-step guide on how to balance your radiators.

If a build-up of sludge is causing an uneven distribution of heat, this can’t be fixed by bleeding out or balancing the radiator. To fix a radiator that is warm at the top and cold at the bottom, the process is different.

How Do You Fix a Radiator Cold at the Bottom?

There are a few different ways you can fix a radiator cold at the bottom. Provided the issue is due to a build-up of sludge, the following methods can be used to resolve the problem

• A powerflush
• A chemical flush

Both a powerflush and a chemical flush need to be carried out by a professional, so you shouldn’t try these methods yourself. We’ll explain what’s involved, but do seek the help of a qualified professional to carry out a powerflush or chemical flush. Book a Hometree engineer.

A Powerflush

A powerflush is used to remove debris from your pipes and radiator, and will typically take between six to ten hours. However, the exact length of time it takes will depend on the heating system.

While you’ll need the expertise of an engineer, for those interested in how the process works, we’ve detailed the steps below:

• You’ve noticed your radiator is cold at the bottom.
• Call a qualified engineer for help, who will come round to carry out the powerflush.
• The engineer will attach a pumping unit to the central heating system. This enables cleaning chemicals to flow through the system – clearing build-ups of sludge.
• The contaminated water will be removed and then disposed of.

Once the powerflush is complete, the radiators should warm up evenly again. You can find even more details about a powerflush by reading our guide ‘what is a powerflush?’.

A Chemical Flush

A chemical flush is considered a basic alternative to a powerflush. As the name suggests, chemicals are flushed through the heating system. Unlike a powerflush, a chemical flush doesn’t require the use of a pump.

Chemical flushes might be worth considering if there are only cold spots in one or two of your radiators. They can also help if you’ve recently had a powerflush, and are tackling smaller build-ups of sludge.

How to Prevent Your Radiator Not Heating Up at the Bottom

There are a few different ways you can prevent your radiator from staying cold at the bottom while hot on the top, including the following:

• Add inhibitor – this is a chemical that’s added to your central heating system, preventing sludge and limescale from building up in your radiator.
• Install a magnetic boiler filter – these filters can collect the debris that would otherwise develop into sludge, preventing your radiator from working effectively.

Tackling the problem effectively with a powerflush or chemical flush can help you keep your heating system running smoothly.

You can also stay prepared for any damages to your heating system by taking out our boiler insurance – which covers repairs to your radiators. Find out more about what’s covered with the Hometree Boiler Cover & Central Heating Plans.