We were getting a new cooker installed for mother-in-law. I got down to the flat and the van was there. I ran round to the flat and the cooker was already there wired in. I ran back outside and caught the driver as he was leaving. I asked if it was installed and he said yes all OK and he left.
I went back in and decided I better try the cooker, I had to remove the packing in the oven and on the door etc. Then I put on the oven circuit breaker in the cupboard and switched on the cooker switch in the kitchen - BANG! - tripped the cct breaker. I thought about phoning them, but knew it would be hopeless as I didn't have the number of the van and the help desk would take ages.
I went home and got tools. Investigated and found they had wired the cooker up wrongly, connecting the Live and Earth together and the Neutral to the ground connection.
Fixed the wiring and now all OK.
Lesson - Never trust anyone but yourself.