Hi,

Your geyser unit must be protected by E/L. This is for shock prevention as water is a direct conductor for electricity. If the geyser is not connected to the E/L it is illegal and very unsafe for your family.

The trip problem is caused by a neutral to earth problem and your earth leakage tripping is protecting you from danger

Yes, they cause for the earth leakage tripping can be they geyser wise system but also check
1. The supply circuit to the geyser (especially the extension point between the old and new wire)
2. And check your element and thermostat

Good luck
Wouter