When the heating is on but your home still feels cold, it’s frustrating, and it’s one of the most common issues homeowners face during winter. Many people search online asking, “Why is radiator not heating up?” The good news is that some causes are simple to fix, while others just need professional attention.
Common Reasons a Radiator Isn’t Heating Up
If your radiator is cold or only warm at the bottom, there are a few likely explanations:
1. Trapped Air
Air can get trapped inside radiators, stopping hot water from circulating properly. This usually causes the top of the radiator to stay cold. Bleeding the radiator with a radiator key often solves the problem quickly.
2. Sludge or Debris Build-Up
Over time, sludge and rust can build up inside radiators, particularly in older systems. This can cause uneven heating or leave the radiator cold altogether. If you’re asking why is radiator not heating up but the pipes are hot, sludge is often the cause.
3. Faulty Thermostatic Radiator Valve (TRV)
If the valve on the side of your radiator is stuck or broken, it may be preventing hot water from entering. Gently adjusting or freeing the valve can sometimes help, but faulty valves often need replacing.
4. System Imbalance
If some radiators heat up while others stay cold, your heating system may need balancing. This ensures hot water is distributed evenly throughout your home.
5. Low Boiler Pressure
Low boiler pressure can stop radiators from heating properly. Check your boiler gauge; most systems should sit between 1 and 1.5 bar when cold. Low pressure is a common reason people ask why the radiator is not heating up across the whole house.
When You Can Fix It Yourself
You may be able to resolve the issue if:
- The radiator needs bleeding
- Boiler pressure is low and needs topping up
- A TRV is stuck but not damaged
Always follow manufacturer instructions and never force components.
When to Call a Professional
If radiators stay cold after bleeding, keep losing heat, or show signs of sludge or leaks, it’s time to call an expert. Persistent problems often point to internal system faults that require specialist tools and experience.
At PES Heating and Plumbing, we regularly help homeowners who are searching “Why is radiator not heating up?” Our domestic plumbers can quickly diagnose the issue and get your heating working safely and efficiently again.
If your radiators aren’t performing as they should, don’t ignore it; early action can prevent bigger, more expensive problems later.
