First I must say albeit competent I am not an electrician. And having not experienced thatI can't say I accept the plastic is expanding, that would only happen with heat and light switches are supposed to get hot, and I would be very concerned if any of my light switches got hot, only one that's a dimmer but only gets warm and fitted by electrician.
Colour code for U.K Old colour for live RED new colour BROWN.
OLD colour for neutral BLACK NEW colour BLUE
Old colour for Earth GREEN NEW colour YELLOW AND GREEN. bare earth wires must be sleeved with yellow and green sleeving never tape.
Sounds to me to be faulty switch and is arcing accasionally so either the terminal/s are loose or the switch needs changing. I'd go for changing the switch. Arcing is evident by black burn marks so check it out. TURN OFF THE LIGHTS AT THE CONSUMER UNIT [FUSE BOX]. Carry out a secondary test using the screwdriver type neon tester at the switch before touching the wires as this will ensure you've turned off the lights for the bathroom, the tester is obtainable at all DIY and electrical shops [buy new switch at the same time]. If you are unsure how to use the tester ask at time of purchase.
If you are unsure what to do then you'll have to call an electrican, ensure he/she is Part P registerd.
For those who say you can't change the switch
U.K Part P rules as searched on internet.
Say you can undertake the work
yourself to BS7671, there is no need to inform
building control, however NICEIC would
recommend you use a registered electrician
to carry out any electrical work in your home
NOTE: This relates to replacing existing one for one NOT for adding fittings
Bob
December 2009
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