In this guide
A radiator that is not heating can make a room uncomfortable quickly, especially when the rest of the heating is running. The useful first step is to notice the pattern. Is the radiator cold throughout, cold only at the top, or is it the only one in the house that is not warming up? Those details can point you towards the right next check without assuming there is one simple cause.
Start with the heat pattern
A radiator that is cold all over can suggest a different issue from one that is warm at the bottom but cold at the top. It also matters whether the problem affects one radiator or every radiator in the home. Treat these signs as useful clues, not a diagnosis. They help you decide whether to look at the individual radiator or the wider central-heating system.
When the top of a radiator is cold
If the lower part of a radiator is warm but the top stays cool, trapped air may be restricting the circulation of hot water inside it. In that situation, the next useful read is How To Bleed A Radiator: A Comprehensive Guide. It covers the task in more detail, including the preparation and wider heating-system checks that matter.
Do not assume that every partly cold radiator has the same cause. If the problem persists, affects several radiators or comes with another heating fault, it is sensible to seek system-specific advice.
When one radiator stays cold
If the rest of the house is heating normally but one radiator is not, the issue may sit with that radiator’s flow. A radiator has a control valve and a lockshield valve, and a closed, stuck or unsuitable valve setting may affect the amount of hot water reaching it. An imbalanced system can also leave one radiator receiving less flow than the others.
These are possibilities rather than a reason to force, dismantle or replace a valve. For a clearer explanation of the parts involved, see Radiator Valves Explained - The Ultimate Guide. If a replacement has been confirmed as appropriate for your system, you can then explore the Radiator Valves range.
When every radiator is cold
If every radiator is cold, the problem may be wider than an individual valve or radiator. Low system pressure, a circulation problem, a thermostat issue or another boiler or central-heating fault can all be relevant possibilities. A boiler fault indication, a leak, or uncertainty about the wider system is a good reason to contact an appropriately qualified heating professional.
Choose the safe next step
Start with what you can observe: where the radiator is cold, whether the rest of the heating works and whether there are signs of a wider fault. Use the linked guides where they fit the symptom you can see, but avoid opening the system, working on the boiler or forcing a valve. A persistent problem is best assessed with the real system in front of the person carrying out the work.