Why Your RCD Keeps Tripping
It is doing its job. The question is what it has found — and repeatedly resetting it is not the answer.
An RCD trips when it detects current leaking to earth. That is precisely what it is for, and a tripping RCD has usually just prevented a shock.
Find the Circuit First
Turn everything off, reset, and bring circuits back one at a time. When it trips, you have your circuit. Then unplug everything on that circuit and repeat. About half the calls we take end here, with a failing appliance rather than a wiring fault.
The Usual Suspects
Kettles, washing machines, immersion heaters and outdoor equipment, in roughly that order. Anything with a heating element eventually develops enough leakage to trip a sensitive device. Outdoor sockets and garden lighting after heavy rain are the seasonal favourite.
Cumulative Leakage Is Real
Every appliance leaks a tiny amount to earth. Enough of them on one RCD and the total approaches the trip threshold, so the circuit trips with nothing actually faulty. The fix is splitting the load across more devices, which usually means a consumer unit change.
What Not to Do
Do not hold the switch, do not fit a higher-rated device, and do not keep resetting it repeatedly. If it will not stay in, leave that circuit off and ring someone. A circuit being off is an inconvenience; the thing the RCD is protecting you from is not.