Why Your Radiators Aren’t Heating Properly
Why Your Radiators Aren’t Heating Properly (And How to Fix It)
If your radiators aren’t heating up properly — or some are hot while others stay cold — you’re not alone. This is one of the most common heating issues we see, especially during colder months. The good news is that many radiator problems are easy to identify, and some can even be fixed without calling an engineer.
Below, we’ll walk you through the most common reasons radiators don’t heat properly, what you can safely check yourself, and when it’s time to call in a professional.
1. Air Trapped in the Radiator
The problem:
If the top of your radiator is cold while the bottom is warm, trapped air is usually the cause. Air prevents hot water from circulating properly.
How to fix it:
Bleeding the radiator releases trapped air.
Steps:
Turn your heating off and let the radiators cool.
Use a radiator key to slowly open the bleed valve.
When air stops hissing and water starts flowing, close the valve.
Check your boiler pressure and top it up if needed.
👉 This is a simple DIY fix for most homeowners.
2. Sludge or Debris Build-Up
The problem:
If the bottom of the radiator is cold but the top is warm, sludge may be blocking the flow. This build-up forms over time from rust, dirt, and debris inside the system.
How to fix it:
Individual radiators may need flushing.
In more severe cases, a power flush of the entire heating system may be required.
⚠️ This should be carried out by a qualified heating engineer.
3. Faulty or Stuck Thermostatic Radiator Valve (TRV)
The problem:
TRVs control how much heat a radiator gives off. If the valve gets stuck (often after summer), the radiator won’t heat properly.
How to fix it:
Turn the TRV fully up and down a few times.
Remove the valve head and gently check if the pin underneath moves freely.
If the valve is damaged, it may need replacing.
4. Heating System Needs Balancing
The problem:
If some radiators heat up quickly while others barely get warm, your system may be unbalanced. This means hot water isn’t being distributed evenly.
How to fix it:
Balancing involves adjusting radiator lockshield valves to regulate water flow.
⚠️ This can be tricky and is best done by a professional to avoid damaging the system.
5. Low Boiler Pressure
The problem:
Low boiler pressure can stop hot water from circulating efficiently, affecting radiator performance.
How to fix it:
Check your boiler pressure gauge.
If it’s below the recommended level (usually around 1–1.5 bar), top it up following the manufacturer’s instructions.
If pressure drops frequently, there may be a leak that needs investigating.
6. Boiler or Pump Issues
The problem:
If none of your radiators are heating properly, the issue may be with the boiler, pump, or controls rather than the radiators themselves.
How to fix it:
This requires diagnosis by a qualified heating engineer to ensure safe and correct repairs.
When Should You Call a Professional?
You should contact a plumbing and heating engineer if:
Bleeding radiators doesn’t solve the problem
Radiators stay cold after multiple checks
Boiler pressure keeps dropping
You suspect sludge build-up or pump failure
Your heating system hasn’t been serviced in over a year
Ignoring heating issues can lead to higher energy bills, breakdowns, or long-term damage to your system.
Need Help with Your Heating?
At ADS Mechanical Ltd, we provide professional plumbing and heating services, including radiator repairs, system balancing, power flushing, and boiler servicing. If your radiators aren’t heating properly, we’re here to help get your home warm again — quickly and safely.
📞 Contact us today to book an inspection or service.