Quick answer
The fault is in the fixed wiring itself, not an appliance. Do not keep resetting it — you need an electrician to test the cables and find the fault.
If your RCD trips even when you have unplugged everything and switched off all lights, the problem is in the fixed wiring — the cables inside the walls, floors, or ceilings. This could be damaged insulation, a cable that has been accidentally drilled through, or moisture inside a junction box. This is a job for a qualified electrician with testing equipment. Do not keep resetting the RCD as repeated resetting can mask a dangerous fault. Switch off the affected circuits at the consumer unit and arrange for an electrician to carry out insulation resistance testing.
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