Tankless water heaters do not require a lot of maintenance, but they do need to be properly cleaned and serviced on a regular basis. If the filter is not cleaned regularly, it can become clogged and affect the performance of the water heater. You will need to flush the unit and clean the filter at least once a year.
They also need special care during winter. If the water heater is not properly winterized, it can freeze and damage the unit.