The girlfriends dad rings me up the other day saying theyve got no upstairs lights in the house working! I asked him if the MCB had tripped maybe due to a lamp blowing? He said no the MCB is switched on! ok so I said id come and have a look for him, so the first thing i checked was if there was power on the circuit side of the MCB, my voltage indicator was showing 0V! Strange the MCB was on, I switched the MCB off then on and retested, now showing the correct voltage! I later found out that my girlfriend had switched her bedroom light on first thing in the morning and a lamp had popped in the fitting and tripped the lights, but she didnt decide to tell me that! Quite an easy fault the breaker had tripped but not operated the switch on the front, must be a faulty mechanism! I changed the MCB for a new one just to avoid any confusion if it was to happen again, never came across this myself!