Bathroom light RCD tripping is usually caused by moisture in a light fitting, a shaver socket fault, or an extractor fan issue — all need to be checked and repaired.
🏠Homeowner view
Bathroom lights that trip the RCD almost always involve water or moisture. The most common cause is a light fitting that's not sealed properly for a bathroom environment — steam from showers and baths gets inside and creates a leakage to earth. Other causes include a faulty shaver socket, a failing extractor fan, or an old sealed unit (heat lamp/bathroom heater combo) that's collected moisture. Try switching off the bathroom circuit and seeing if the RCD stays on. If it does, isolate each bathroom item one by one — light, shaver socket, extractor — to find which is leaking. Once you've identified it, call an electrician to replace it. Never use an ordinary room light fitting in a bathroom — all fittings must be rated for wet/damp locations (IP44 or IP65 depending on the zone).