If your boiler is on but one or more radiators aren’t heating up, you’re definitely not alone. This is one of the most common heating issues we get called out for especially during colder months when radiators are working overtime. While it can feel frustrating, the good news is that most radiator problems have simple explanations, and some can even be fixed without professional help.
In this guide, we’ll walk you through the most common reasons radiators stop working, what you can safely check yourself, and when it’s time to call a qualified heating engineer to prevent bigger (and more expensive) issues.
Why Your Radiator Might Not Be Working
If your boiler is running but the radiator still feels stone cold, it normally comes down to one of the following issues:
1. Air Trapped in the Radiator
This is by far the most common issue we see.
When air gets trapped inside the radiator, hot water can’t circulate properly. You’ll usually feel heat at the bottom but not at the top, or the radiator may stay cold altogether.
Symptoms:
Gurgling or hissing noises
Top of radiator cold, bottom warm
Heating is slow to warm up
Fix:
Bleed the radiator using a radiator key. This releases trapped air and allows hot water to fill the radiator fully.
2. Radiator Valves Stuck or Closed
Every radiator has valves that control water flow. Over time, these valves can get stuck, especially if the system hasn’t been used for a while.
Symptoms:
Radiator cold while others are hot
Valve difficult to turn
TRV (thermostatic valve) stuck in one position
Fix:
Check that both valves are open. If a thermostatic valve is stuck, gently tapping it may release it but be careful not to force it. If it won’t move, we can help repair or replace it.
3. Sludge or Debris Build-Up in the System
Another extremely common issue: sludge.
Sludge is a mix of rust, debris and limescale that settles at the bottom of radiators and pipes. It restricts water flow and reduces heat output.
Symptoms:
Radiator warm at the top but cold at the bottom
Discoloured water when bleeding
Radiators taking ages to get hot
Boiler making kettling noises
Fix:
A power flush or chemical flush by a professional is the best way to clear the system and restore efficiency.
4. Boiler Pressure Too Low
Your boiler relies on correct pressure to circulate hot water around your radiators. If the pressure drops, the system won’t heat properly.
Symptoms:
Boiler pressure gauge below 1
Radiators partially cold
Heating cutting out intermittently
Fix:
Most boilers allow you to top up the pressure via the filling loop. Always check your manufacturer’s guidelines. If the pressure keeps dropping, you may have a leak and should call an engineer.
5. Problems With the Circulating Pump
The pump is responsible for moving hot water around your system. If it’s faulty or set too low, radiators won’t heat evenly.
Symptoms:
All radiators lukewarm
Pump making unusual noises
Heating slow across the entire property
Fix:
Pumps may need adjusting, repairing, or replacing. This is definitely a job for a qualified engineer.
What You Can Try Before Calling a Professional
Here are some safe, simple checks you can do:
- Check that the boiler is switched on and showing no error codes. Sounds basic, but it’s a very common oversight.
- Make sure the heating is actually turned on. Check your thermostat, programmer, or smart controls.
- Feel the radiator valves. Ensure both inlet and outlet valves are open.
- Bleed your radiator. If you hear air escaping, that was the problem. Retest once complete.
- Look at your boiler pressure. If it’s below 1 bar, repressurising may solve the issue.
If you’ve checked these and the radiator is still not heating properly, it’s time to call an expert continuing to run the system with a fault can cause bigger issues like pump failures, boiler lockouts or long-term system damage.
When to Call Us and How We Can Help
If your radiator isn’t heating properly, some issues require specialist tools and professional expertise. Whether one radiator never heats up, multiple radiators stay cold, your boiler keeps losing pressure, TRVs are broken or leaking, or you suspect sludge or a noisy circulating pump, it’s always safer to call a qualified engineer rather than risk further damage. We work with all boiler types, combi, system, and conventional and can quickly diagnose what’s going wrong.
Once we’re on site, we’ll carry out a full diagnosis of your radiator and boiler system, checking valves, pipework, pressure, pumps, and circulation to find the root cause efficiently. If your system is suffering from sludge or debris, we can perform a chemical or power flush to restore full heat output. We also replace faulty thermostatic radiator valves and lockshield valves to improve efficiency and allow better temperature control, repair or replace pumps to ensure proper circulation, and service and optimise your boiler to reduce breakdowns and lower heating costs.
With fast, same-day callouts, we make sure your home or business is warm again as quickly as possible, providing a safe and lasting solution for your heating problems.
Get Your Radiator Working Again, Professional Help When You Need It
If your boiler radiator is not working, don’t struggle through the cold or risk damaging your heating system by trying every DIY fix. We handle these issues every day, and we can get your radiators working efficiently, safely and quickly.