Tankless Water Heaters in Portland & Southern Maine

A tankless unit is rated by how many gallons per minute it can heat to the desired temperature rise, not by storage capacity — there isn't any. If two showers and a dishwasher run simultaneously and their combined flow exceeds the unit's rated capacity, everyone gets lukewarm water, not an empty tank. Sizing correctly means adding up realistic simultaneous demand for the household, not just picking the biggest model available.

Gas-fired tankless units draw significantly more gas flow at the moment of use than a tank water heater's burner, which sometimes means an existing gas line needs to be upsized to feed it properly — a detail worth confirming before assuming a straightforward swap. They also require their own dedicated venting, typically a sealed PVC or stainless vent system rather than a shared chimney flue.

Tankless units accumulate mineral scale on their internal heat exchanger, especially in hard-water areas, and manufacturers specify periodic descaling — flushing the unit with a descaling solution — to maintain flow and efficiency. Skipping this is the most common reason a tankless unit's performance degrades over time, since there's no tank sediment to blame instead.

Navien — NPE-A2 and NPE-S2

Navien's condensing NPE-A2 and NPE-S2 lines show a numeric code on the digital remote (or the unit's own display) when they lock out. Navien doesn't publish one cross-model code chart — the meanings live in the manual for that specific series — so we pull the manual for the exact model and check the unit's stored error history, which most Navien controllers keep, rather than work from a generic list.

Rinnai — Residential Tankless

Rinnai is direct about this on its own FAQ: error codes vary by product, and the company points owners to the unit's installation manual or Rinnai support to trace a code to its cause rather than publishing one universal chart. The code shows on the digital remote controller. We confirm the code against the manual for that specific model before recommending a repair.

Noritz — NR83DVC, NR98DVC, NR98SV

Noritz is the exception — it runs a public, plain-language knowledge base for its common codes. These apply to the direct-vent condensing and standard copper-heat-exchanger models most often installed in homes; check the data plate for the exact model first.

Rheem — IKONIC, RTGH, RTG-R, ThermaForce

Rheem's current residential tankless lines — IKONIC, RTGH, RTG-R, and ThermaForce — all run a self-diagnostic program, but Rheem documents the specific fault codes inside each model's own owner's manual and service bulletins rather than one shared chart. A code on one Rheem line can mean something different on another, so we match the installed model to its own bulletin before diagnosing.

Takagi's non-condensing units display a numeric code on the remote, or a flashing red LED on the board itself, depending on the model. Unlike most of the brands above, Takagi's own troubleshooting guide lists these plainly.