The "first black switch on the right" is is an RCD (Residual Current Device.)Picture of the consumer unit attached. The first black switch on the right, immediately to the left of the two red main switches, trips.
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(The next five "switches" are MCBs (Miniature Circuit Breakers) and you have FIVE of these "protected" by ONE RCD (Residual Current Device)
The use of ONE RCD "protecting" FIVE MCBs leads to the problem which you experienced and which "plunged the house into darkness. " (THREE other circuits - anyway!)
Last night, somewhat bizarrely, it tripped at about 21h30 and plunged the house into darkness.
Apart from you problem with "steam" causing sufficient leakage (somewhere) to cause an RCD to "trip", you have a Consumer Unit where multiple circuits are protected by ONE RCD, which causes another problem, when such an RCD is activated.
To avoid this in the future, it would be best if the two RCDs were removed and the RCDs replaced with RCBOs (Residual Current circuit Breaker with Overcurrent protection) - (See Post #4.)
Unfortunately, this will come at a cost (for replacement equipment - at least.)
However, if 10 RCBOs had been installed (in lieu of 10 MCBs plus 2 RCDs) in the first place, the cost may not have been significantly greater and the inconvenience of a fault on one circuit inactivating several other circuits would not exist.
(As an "aside", in Australia it is not allowed to have more than three circuits "protected" by one RCD.)
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