Why has my bathroom light stopped working?

Start by checking whether other lights in the house are working — if not, the circuit has tripped. Go to the consumer unit and reset the tripped MCB. If other lights are on, the most likely cause is a failed bulb. Check the MCB for the lighting circuit is on. If the bulb is fine and the circuit is on but the light still does not work, there may be a fault in the fitting, the pull-cord switch, or the wiring. Bathroom lights are in a zone where moisture can damage electrical fittings over time — steam and condensation cause connections to corrode. Do not replace a bathroom light fitting yourself — bathroom zones have specific wiring regulations and the fitting must be IP-rated. Call a qualified electrician.