This page is about the narrow case: you already have a tankless heater, it has failed for good, and it needs to come off the wall and be replaced with another one. That is a different job from a first time conversion, because the gas line, the venting and the water connections already exist and were sized for a tankless unit.

A tankless heater reaches genuine end of life when the heat exchanger goes. That is the copper or stainless core the water actually runs through, and when it corrodes through or scales beyond recovery, the cost of the part approaches the cost of the whole appliance. Control boards on obsolete models can put a unit in the same position, when parts simply are not made anymore.

What we will not do is call a unit dead because that is the easier conversation. Plenty of tankless heaters get replaced when a descale, a flow sensor or an igniter would have brought them back. We check that first and tell you what we find, even when the answer means a smaller invoice.

Heat exchanger failure is the usual verdict. Years of mineral scale from our well drawn supply, combined with the thermal stress of firing hard and shutting off dozens of times a day, eventually opens a pinhole or thins a passage past saving. Once water is leaking out of the exchanger itself, that is the appliance, not a part.

Obsolescence is the quieter one. Tankless units are controlled by circuit boards, and manufacturers stop making boards for discontinued models. A unit that is mechanically sound but cannot get a controller is finished regardless of how healthy the rest of it looks, and there is no cleverness that gets around it.

Neglect accelerates both. Units near the coast and in rental homes on 30A frequently run for years without a single flush. The manual’s flush interval assumes typical water, and ours carries more mineral than that assumption. A unit descaled on a sensible schedule commonly outlives one that never was by a wide margin, which is a maintenance argument rather than a sales argument.