1400W isn't a tankless (too low wattage to give enough heat for an instant-heat).

In your case: rarely used (sink only) a point of use 3kW is the right choice. It doesn't require any motion sensor because it starts heating only when hot water is flowing and stops as soon as water is turned off.

I suggest you, if you don't want to change your water heater, to add a timer instead.
Timer that kicks in the boiler once (or twice) a day for 2 hrs that is enough time to heat water with this timings 04:00->06:00 and 11:00->13:00. Because at least one hour is needed to warm up all the water (10L if it's a small size) and, once heated, water will stay hot for some hours.

1400W isn't a tankless (too low wattage to give enough heat for an instant-heat).

In your case: rarely used (sink only) a point of use 3kW is the right choice. It doesn't require any motion sensor because it starts heating only when hot water is flowing and stops as soon as water is turned off and can be plugged to a 30A circuit.

I suggest you, if you don't want to change your water heater, to add a timer instead.
Timer that kicks in the boiler once (or twice) a day for 2 hrs that is enough time to heat water with this timings 04:00->06:00 and 11:00->13:00. Because at least one hour is needed to warm up all the water (10L if it's a small size) and, once heated, water will stay hot for some hours.