Hot water heater problems?

Many water heaters (US AND ABROAD) have two thermostats. Thermostats frequently do go bad, most likely if the thermostat went bad it was because of heat damage which would have been caused by a bad element, did upper and lower thermostats have high limit switches (reset buttons) or did only the upper ? Did you replace thermostats like for like or did you buy a universal replacement? Look at the wiring diagram on the new thermostat and compare it with the diagram on the tank, read sidenotes on the new thermostat ,use a multimeter to determine if both elements are being energized at the same time, a different thermostat wired incorrectly may energize both elements at the same time which draws too much power which trips the breaker, test elements with ohms reader on multimeter or remove and inspect for damage ,replace if necessary ,if thermostats continue to be an issue ,replace with original type and wire according to original wiring diagram or provide more information

You changed the wrong parts. The reason the thermostat was tripping was because one of the heating elements inside has been compromised. The outer jacket of the element has most likely developed a hole in it and it is shorting into the water. You need to replace the elements!

Since the one has gone, it is a good idea to replace both of them.

You have two thermostats on one water heater? Very interesting. In the US, there is only one thermostat for one water heater. Anyway, you've replaced the wrong thing. You should have replaced either the elements or the entire unit. Thermostats rarely go bad. You're arcing out to ground, that's the noise you're hearing.

when you say thermostat you mean aquastat?sounds more like you have a heating element issue probably corroded and broke the elements open try replacing those.if you have a voltage meter you can ohm them outby going across both leads and if your meter beeps when you touch both ends of the element with your leads then the element is probably good.vif no beepmreplace the elements

Most likely the heating coil/resistence is corroded leading to poor performance and then a short circuit. Change it too.

i think you need a new water heater. btw hot water doesn't need to be heated