Check Amazon Price. Another great product from Bosch, the Ariston unit is one of the best 13 amp under sink water heaters on the market. It has a larger tank, which can hold up to 4 gallons. This makes it great for larger jobs such as running multiple showers or sinks simultaneously. Make sure you adjust both the upper and lower thermostat is you have two of them and make sure the temperature in both matches or the top thermostat can be a few degrees above the lower thermostat. Put all your insulation back and put the control panel back in its original position. Go to your circuit breaker location and flip your power back Manage and control your Ariston products easily and wherever you are: Set a schedule. Change operation mode. Control your heating and hot water temperature. Adjust your indoor temperature based on your location. Ensure your heating is on only when you need it. Find out Ariston Net Smart Functions. VjyF6.