Went to switch the bedroom light on this morning and it went straight off. Checked the landing light and that was off too but downstairs lights and sockets were all ok. Lamp blown tripping the upstairs lighting circuit I thought, but no, the breaker was not tripped. Tried turning it off and on but made no difference, then had to run cos I needed to get off. Just got home now and need to tackle it after getting some grub but no idea where to start. Whole upstairs circuit is out, but if it gives any clue, the bathroom light LEDs are faintly lit with residual current which disappears when I turn the switch ON. Any pointers?