Navien tankless water heater code E016: Heat exchanger overheated

1. A one-off overheat that clears once the heat exchanger has cooled down.

   Switch a Navien water heater off for 30 minutes to cool downYou can do this

   1. Turn the water heater off with the Power button on its front panel, or on the remote controller for outdoor NPN models.
      If the heater overheats or the gas will not shut off, close the manual gas valve to the heater.
   2. Leave it off for at least 30 minutes, then turn it back on.
   3. If the code comes back, move on to the next check listed for the code, such as cleaning the cold water inlet filter.

2. A blocked cold water inlet filter is cutting the flow of water through the heat exchanger.

   Clean the cold water inlet filter on a Navien water heaterYou can do this

   1. Put a bucket under the heater. Turn the heater off with the Power button, close the gas valve to the heater by its handle, and close the cold water supply valve on the heater's inlet (or the water main if there is no valve).
      The heater can stay hot for several minutes after it is switched off. If you smell gas at any point, leave the building and call your gas supplier from elsewhere.
   2. Open all the hot water taps in the house so the water in the pipes drains out.
   3. Unscrew the cold water inlet filter from the bottom of the heater and let the water drain into the bucket. On NPE-A and NPE-A2 models, also take out the recirculation inlet filter and open the pump drain plug. On NPN models, open the water drain plug.
   4. Rinse the filter (or filters) under clean cold running water, scrubbing with a brush if needed.
   5. Refit the filters, tighten them, and close the drain plug.
   6. Refill by reversing the draining steps. Open the cold water supply valve, close the hot taps once water runs from them, open the gas valve and turn the heater back on.

   Clear a Navien error codeYou can do this

   1. Deal with the cause first, using the checks listed for the code.
   2. On NPE-A2 and NPE-S2 models, press the Back button on the front panel. On first-generation NPE-A and NPE-S models and on indoor NPN models, press the Reset button on the front panel.
   3. If an NR-21DU remote controller is fitted, you can press its OK button once instead. On outdoor NPN models, which have no front panel, the remote is the way to reset. The remote shows RST when the error is reset.
   4. If the code comes back, stop resetting. Note the code and the model number and contact Navien technical support or a licensed technician.
      Resetting over and over can hide a fault that needs a technician.

3. Scale has built up inside the heat exchanger and needs flushing out.

   Flush the heat exchanger on a Navien water heaterYou can do this

   1. Navien calls this a somewhat complicated job. If you are unsure about any step, book a licensed technician instead, as poor maintenance can void the warranty. It needs service valves with drain ports on the hot and cold water lines at the heater, as in Navien's diagram; if yours has none, book a plumber.
   2. Gather a bucket of 5 gallons or more, cleaning solution diluted with water, three hoses and a water circulation pump.
   3. Turn the heater off with the Power button and unplug it, or switch it off at its power switch or breaker if it is wired in. Close the shutoff valves on the hot and cold water lines (C and D in Navien's diagram).
   4. Run a hose from the hot side drain port (A) into the bucket. Connect the pump outlet to the cold side drain port (B), and put a hose from the pump inlet into the bucket.
   5. Pour the cleaning solution into the bucket, open drain ports A and B, and run the pump for at least 45 minutes.
   6. To rinse, move the hose on port A from the bucket to a drain. Close port B, open the cold shutoff valve D (leave the hot shutoff C closed) and let water run through for 5 minutes. Then close port A and open valve C.
   7. Close the shutoff valves C and D again. Disconnect the hoses, unscrew the cold water inlet filter, clean out any residue and screw it back in firmly. Then open valves C and D.
   8. Plug the heater back in, or switch the power back on, and turn it on with the Power button.

   Have the heat exchanger flushed and descaled

4. A fault that needs a technician. Suspect this when the code keeps coming back after the filter is clean and the heat exchanger has been flushed.

   Book a licensed gas technician

Booking a licensed gas technician