My Laguna garden water pump stopped working all electrical problems have been eliminated

This is always caused by bad treatment after use. You need to wash it, pump soapy water, then rinse and wash out the the bottle, then push clean water through. Finally empty it and pressurize it and blow all the water out so you have a clean dry final unit. My one gallon sprayer is 12 years old.

Take it all apart and soak it in hot soapy water.

I do not know this model but it sounds like a bad or missing gasket/o-ring.

It almost sounds as if the thermal load protection fault is being tripped on the pump. When the pump kicks off is the housing extremely warm? If so you may need to replace the pump.

https://www.kaercher.com/int/support/service/downloads/operating-manuals.html

Problem here ?? what type of laguna as up till about 99 it was a manual hydraulic engine driven pump later ones had a electric over hydraulic unit at the front right side just behind the bumper ,top up on top of the unit later models have a electric motor under the dash with no hydraulics but a direct drive to the steering column which needs special software to reset the straight ahead position but this is a renault the pain vehicle of my life ,best advice is to buy a old XJ6 sovereign jag if your mileage per year is low

ck electric side of key switch may be over heating and then cools off and runs again, relay can also do this. then ck anti theft.

Possible causes: Electrical or Mechanical. For Electrical - Check to make sure power is coming to the outlet/cord it is plugged into. If there is a GFCI on the circuit, make sure it is reset.
Mechanical: If something got sucked into the pump it may have caused the impeller to stop and/or the pump to overheat. Some models have an thermal override that will shut the pump off if it overheats. If it is a magnetic drive pump, the impeller can probably be saved, if it is a direct drive, it may have gotten damaged by the jam. Unplug the pump and carefully disassemble the portion where the water goes in to determine if something got sucked into the impeller mechanism.

Your problem is the thermal switch is tripping off. this means there is some supply or voltage problem. Most likely fix is replacing the capacitor.

That is a great question.
The only things that I can think of are installing a valve or raising the discharge line higher than the water level in the tank.
The valve could be hand operated or electrically operated to shut when the pump stops.
Also, if you could run the pump discharge up to a point higher than the water line and install a vacuum breaker at this point and run the line back down to where you use the water, when you shut the pump, the siphon suction would open the vacuum breaker admitting air and stopping the siphon.
Let me know what you end up doing.
Gary

electric pump ,buy a new one 554 euros plus tax