Why Is My Radiator Cold at the Bottom? And How to Fix it?

If your radiator is warm at the top but cold at the bottom, you’re not alone. This is one of the most common issues homeowners experience with their heating system, especially during colder months. In this article, we’ll explain the typical causes behind this issue and what can be done to fix it.

1. Sludge Build-up Inside the Radiator

The most common reason for a radiator being cold at the bottom is sludge. Over time, rust and debris can form in your central heating system. This build-up settles at the bottom of your radiator, preventing hot water from flowing properly.

How to know it’s sludge:

  • Radiator takes longer to heat up
  • Bottom remains cold while top is warm
  • Noises coming from the system
  • Discoloured water when bleeding the radiator

What can you do?
A heating engineer can carry out a system flush to remove the sludge. In many cases, they may also recommend installing a magnetic filter to prevent the problem recurring.

2. Trapped Air

Another reason is trapped air inside the radiator. This disrupts water circulation and prevents the entire surface from heating evenly.

What can you do?
You can try bleeding the radiator using a radiator key. Be sure to switch the heating off before doing this. If the radiator doesn’t warm up evenly afterwards, the issue may be more than just trapped air.

Woman dressed in winter clothes trying to warm up near a broken radiator in a UK home

3. Radiator Valves Not Working Properly

If your radiator valves are stuck or faulty, the flow of water into the radiator may be restricted.

What can you do?
Make sure both the thermostatic and lockshield valves are open. If they seem damaged or blocked, a plumber can check them and replace if necessary.

4. Your Heating System May Need Balancing

When some radiators heat up faster or slower than others in your home, it may be a sign the system is unbalanced. This means water isn’t flowing evenly across all radiators.

What can you do?
A qualified plumber can balance your system by adjusting each radiator’s lockshield valve, ensuring an even distribution of heat throughout your home.

When Should You Call a Professional?

If bleeding the radiator doesn’t solve the issue, or if your heating bills seem high despite poor performance, it’s time to call in a professional.

Leaving issues like sludge untreated can reduce the efficiency of your entire heating system and cause long-term damage.

Professional Help in Kent

At Daniel Emergency Plumbing Ltd, we handle radiator issues across Ashford, Maidstone, Canterbury and nearby towns. Whether your heating problem is minor or urgent, our team is available 24/7 to get things running properly again.

We specialise in:

  • Radiator repairs
  • Central heating troubleshooting
  • Power flushing
  • Valve replacement and system balancing

Need fast help?
Call 01233 51 6246 or request a callback via our Contact Page

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