Quick answer
Navien error code E515 means abnormal operation of the PCB: the control board has failed a self-check. The heater is unreliable until the cause is found; it may run after a reset and fail again. Confirm the power cord is in a properly grounded outlet and power-cycle once. If E515 comes back, the board and its wiring need testing before a replacement board is ordered.
The PCB is the printed circuit board that runs the heater, and Navien error code E515 means abnormal operation of that board. It checks itself as it works, and E515 is what it posts when one of those self-checks fails. The code tells you less than most do, because the part reporting the fault is also the part under suspicion. The meaning is taken from the NPE-2 user manual; other Navien series number their codes differently, so trust the label inside the panel of your own unit first.
Will a Navien run with E515, and should it?
Sometimes it will, and that is the trap. A reset often clears E515, and the heater makes hot water for a day or a week before the code returns. Treat the unit as unreliable until the cause is found: a board that fails its own checks can drop out mid-shower, or on the coldest night of the year, when the heater's freeze protection depends on it.
Check the outlet and power-cycle once
The manual's listed action for E515 is to confirm the power cord is plugged into a properly grounded outlet.
- The plug should be fully seated in a three-prong wall receptacle, not hanging half out behind the unit.
- Remove any extension cord, power bar or adapter between the heater and the wall.
- Check the breaker for that circuit, and whether anything else on it has been tripping it.
- Turn the heater off, wait a full minute so the board powers down completely, and turn it back on. Do this once.
Write down what was happening when the code appeared: a storm, a flicker, a hydro outage, someone running a large tool on the same circuit. That timeline often names the cause before a meter does.
What knocks out a Navien control board
- A power surge or brown-out. Storm-season flickers and the voltage swing as power comes back after an outage are hard on electronics, whether your utility is Burlington Hydro, Alectra or Hydro One.
- A grounding fault. A loose ground or an ungrounded receptacle leaves the board without a stable reference.
- A failed relay or component on the board. Relays switch every time the heater fires, and they wear.
- Moisture in the cabinet. A weeping fitting above the board, condensate that is not draining, or a damp unheated space leaves a film that conducts where it should not.
Why the board gets tested before it gets replaced
A control board is one of the costlier parts in a tankless heater, and replacing it on a guess is an expensive way to be wrong. If a bad ground, a corroded connector or a water leak caused E515, a new board inherits the same problem and fails the same way. So the technician works from the outside in: supply voltage and ground at the receptacle, then the wiring harnesses and their connectors, then signs of water or heat on the board itself.
Only when those check out is a board ordered. It has to be the correct board for the model, set up for that heater, before the unit is fired and tested. On a gas appliance, that final combustion check belongs to a TSSA-licensed technician.
Repair the board or replace the heater?
Use a simple rule. If the heater is under about 12 years old and has been flushed regularly, a board is worth doing. If the repair quote passes half the price of a new unit on a heater older than that, put the money toward replacement; a new tankless runs $3,500–$6,500 installed.
- Diagnosis of a control board fault: $90–$150, credited to the repair.
- Wiring and connector repairs inside the heater: typically within $150–$800.
- A replacement board: quoted in writing by model, since no single figure fits every Navien.
- Grounding at the receptacle or circuit: electrician's work under ESA rules, quoted by the electrician.
After a power outage specifically, why a tankless is not working after a power outage walks through the restart. A flame-signal fault is Navien E004, and the full list is in the Navien error code guide. ZK Mechanical diagnoses and repairs Navien heaters across Burlington, Oakville, Mississauga and Brampton: book tankless water heater repair, call (647) 801-1252, or write to us with the model number and what the display shows.