Do this first
Water escaping from the tank body: turn off the water supply to the system. There is usually an isolation valve on the cold inlet at the tank. This is the single most useful thing you can do, because a failed cylinder keeps refilling and keeps leaking.
A smell of gas: do not touch switches or the appliance. Leave the area, ventilate it if you can do that safely on your way out, and call from outside.
Repeated tripping at the switchboard: leave that circuit off. The safety switch is doing its job, and resetting it repeatedly defeats the protection.
Beyond isolating, leave the system alone. Hot water systems hold water under pressure and involve gas or mains electricity, and both are licensed work for good reasons.



