Tankless water heater often start flashing error codes. Each error code means something. Most common error code is that tankless is due for service. something fails, and homeowner doesn’t know that they need to service their tankless water heater unit every 2-4 years. Maintenance is required for every tankless water heater. Another failing tankless unit is because the tankless has never been sized or it has been installed incorrectly. Pictures show before and after repair of a tankless unit.