[Shower keeps tripping the electrics]what to check

This is the one fault in the category where the appliance is telling you something about safety rather than about performance, and where the instinctive response makes it worse. An electric shower sits on a dedicated high-current circuit, protected by a breaker against overload and, because it is in a bathroom, by a 30 mA residual current device against current leaking to earth. Those two devices trip for different reasons and which one has moved tells you a great deal. A breaker alone usually means current above what the circuit is rated for.

An RCD means current is going somewhere other than back down the neutral, and in a shower there is one overwhelmingly common route for that: the heating element sits in water, and when its sheath fails the element starts leaking to earth through the water itself. The reason this is rated the way it is has nothing to do with the inconvenience. An RCD that trips is a device doing exactly what it was fitted to do, on a circuit that is in a wet room, feeding an appliance you stand inside while wet and barefoot.

Resetting it repeatedly to force one more shower is asking a safety device to keep catching a fault that is still there, and the failure mode people do not expect is that the leakage gets worse gradually rather than suddenly. There is a second cause worth naming because it is not the shower at all: water tracking into the pull cord or the isolator. Both live in a humid room, both have terminals in them, and either will trip an RCD in a way that looks identical from the consumer unit.