A tankless water heater saves space and can last well when maintained, but reliability depends on water quality and routine flushing. Common repairs involve ignition components, flow sensors, control boards, and scaling in the heat exchanger, especially with hard water.
Repair is typically worthwhile for a mid-life unit when the issue is a known service part (igniter, sensor, valve) under the threshold, because replacing the whole system is costly and may require venting or gas line changes. Replacement becomes more attractive when the heat exchanger is compromised, scaling is severe and recurring, or multiple faults appear close together-those can indicate broader internal wear.
If maintenance history is unknown and the unit has frequent error codes, replacement can reduce downtime and restore consistent hot water, especially for larger households.