Why is my electrical cable getting hot inside the wall cavity when the heating runs?

Finding that an electrical cable is getting hot inside a wall cavity when your central heating is running is genuinely concerning, and you are right to look into it. The good news is there are a few common reasons this happens, and understanding them will help you explain the problem clearly to an electrician. The most common cause is thermal insulation. When wall cavities are filled with insulation — whether that is blown-in mineral wool, foam, or rigid boards — electrical cables that run through those cavities can no longer shed heat the way they are designed to. Every cable is rated to carry a certain amount of current, but that rating assumes the cable can cool itself by radiating heat into the surrounding air. When insulation wraps around the cable, that cooling effect disappears, and the cable runs hotter than it should. The heating system itself can make things worse in two ways. First, if your heating pipes run near or through the same cavity, they warm the air around the cable. Second, if your heating system is drawing more electrical current than usual — perhaps a pump or boiler controller is working harder — the cable carrying that load will naturally generate more heat. Other causes worth knowing about include: A cable that is undersized for the load it carries, meaning it was not correctly calculated when installed. A loose connection at a junction box, socket, or consumer unit, which creates resistance and generates localised heat. Multiple cables bundled together without being de-rated, so the combined heat output is too high. Poor-quality or aged cable where the insulation has already begun to break down. What you can safely check yourself is limited, and that is deliberate — wall cavities and live wiring are not DIY territory. You can feel whether a socket, switch, or light fitting connected to that circuit feels warm to the touch, which would suggest the issue extends beyond just the cavity. You can also check whether the problem is recent, perhaps linked to new cavity wall insulation being installed in your home. Call a registered electrician — ideally one on the NICEIC or NAPIT register — as soon as possible. Tell them when the heating runs, which circuit seems affected, and whether insulation has been installed recently. This is not a fault to leave and monitor.