Noritz Tankless Water Heater Code 16 [Why + How To Fix]

The Noritz Tankless water heater code 16 indicates an abnormal rise in the hot water outlet temperature. It may seem like a big issue but in reality, it’s caused by other problems. Here are the most common reasons that are responsible for showing this error code:

  • Scale deposits in the heat exchanger 
  • Clogged water filter 
  • Improperly adjusted manifold pressure
noritz tankless water heater code 16

You’ll have to underlying reason that caused the code and reset the heater to clear the code. We’ll show you exactly how you can do that. So, let’s dive in!

Instant Solutions For Noritz Tankless Water Heater EC-16

Before moving to diagnose in detail, let’s have a look at the below table to see the probable causes and solutions at a glance:

Probable ReasonHow To Fix?
Reaches Temp above your setting temperature> Reset your unit by unplugging it for 1 minute and plugging it back.
Clogged Heat exchanger > Flush the heat exchanger. 
Blocked water filter > Clean the water filter
Improperly adjusted manifold pressure > Adjust the manifold pressure to the right settings

Noritz Tankless Water Heater Code 16 [Reasons + Solutions]

First, try resetting the heater. Sometimes, the error code can appear due to glitches and resetting will solve the issue. If that doesn’t work, then let’s start the diagnosis to clear this error code.

Note: Read our guide on Noritz tankless water heater problems & error codes.

1. Clogged Heat Exchanger

Nine times out of ten, your Noritz water heater displays an error message 16 because of building up scale in the heat exchanger. This type of scale keeps the extra heat inside your water heater. And, it increases the outlet water temperature abnormally which leads to the display of the EC-16.

Plus, this scale restricts the water flow rate as an additional precaution. Finally, the scale overheats the water and increases the temperature of the hot water. 

How To Fix:

To remove EC 16, follow the procedures to descale your unit. To perform flushing steps, first, you will need the following tools:

  •  A plastic 5-gallon bucket
  •  3–4 gallons of food-grade, distilled white vinegar
  • A pair of drain pipes with a 34″ connector
  • An underground/submersible pump

Confirm that the unit is turned on. Find the gas valve by following the supply line, and turn it off.

Shut off the main water valves for cold and hot water and position them parallel to the pipes. (The hot water side is indicated by the red isolator valve and the cold by the blue.)

Remove the drain covers on the hot and cold outlets. Place the bucket so that the heated water side is under it. After that, turn on the red flow control valve, and then use the buckets to collect any water that remains inside the unit. 

You should repeat the same to drain the water to the cold water side.

Now, insert a hose into the submersible pump and the connecting hose into a 5-gallon bucket. Then, attach the pump hose to the cold water inlet valve, making sure to tighten the screw.

The other hose should be connected to a hot water drain valve, and its other end should be inserted into the plastic bucket. Besides, in order to submerge the pump, pour 3-4 liters of food-grade white vinegar into the plastic bucket.

Remember: In this step, you should turn the pump on and plug it into an electrical socket. Let the pump operate for at least an hour.

After an hour, disconnect the pump hose and turn the cold water flow valve back to the off position. Tighten the drain cap after replacing it. Take both the drain pipe and the pump out of the bucket. Next,

  • Empty the plastic bucket of the liquid.
  • Move the drain hose within the drained bucket, and then switch the main inflow valve to the “On” position.
  • Run 20 liters of water through to the hot water side of the unit to flush it out.
  • To drain water from the unit, set a bucket underneath it and unscrew the drain plug.
  • Turn the main cold and hot water valves to the ON position. The gas distribution valve should also be opened fully.

Lastly, tap the power ON/OFF button to switch the device off and back on to clear the error code if it flashes normally.

2. Blocked Water Filter

A blocked water filter or low water pressure is the next major culprit for showing error code 16 with your Noritz water heater.

noritz tankless water heater blocked water filter

Basically, a tankless water heater requires a clean water filter for smooth operation. The hot water won’t function properly if debris clogs the water filter. 

A clogged or filthy water filter slows down the water pressure in the heater and causes the water to exceed the output temperature unexpectedly. However, proper cleaning of the water filter can resolve the problem instantly.

How To Fix:

For a clogged water filter, follow the instructions to clean the filter without any hassle:

First of all, turn the input water supply valve to the right to start the process. The valve needs to be placed horizontally. When the bucket is ready, you should remove the inlet and outlet water caps on the isolator kits. Then you have to open both drain valves. 

Then, take the filter out of the inflow port and wash it with running water. Make sure the filter is properly washed and no debris is there.

wash the noritz tankless water heater's filter properly

You should check the cleaned filter whether is dried to install into the inlet port. Be sure you have closed the drain plugs and replaced the caps. Hopefully, you won’t face any low water pressure with your water heater.

3. Gas Pressure Issues

Last but not least, improper or wrong fuel supply is also a responsive factor for getting the error code 16. When the manifold gas pressure isn’t within the range, the BTUs flow will be too high which spikes the temperature abruptly.

gas pressure issues

So, it is required to check the gas pressure whether it has raised the abnormal temperature via digital manometer. And unfortunately, you will see the code if the output temperature is reaching too high as you set the temperature.

How To Fix:

To solve the gas supply problem, first, ensure you fuel up your water heater with the correct type of gas. So, feed your unit with whatever gas type the unit requires for proper operation, natural or propane.

Then, don’t forget to check out the rating plate of the unit. Inspect the manifold pressure has been adjusted with the digital manometer.

Finally, ensure you have adjusted the manifold pressure according to the manufacturer’s guidelines. You can check out our guide on Noritz tankless water heater code 51 to find out all about it.

We’ve explained how you can check and adjust the manifold gas pressure in detail there. However, if you don’t feel comfortable doing it yourself, you can contact a qualified technician to do it for you.


What may occur if I ignore the EC-16 with my tankless water heater?

Actually, the 16 error code indicates a major precaution for safe operation. If you ignore the abnormal rise in temperature can harm the heater or scald people anytime.

What is the scale in a heat exchanger?

Scale is a substance caused by inorganic salt and dirty water that creates a restriction layer in the heat exchanger of your water heater. Eventually, it can slow down the hot water flow rate.           

How to prevent my water heater from mineral building up on the coils?

When you’re living in a hard water area, the scale may deposit in the coils or the heat exchanger over time. You can use a water softener to prevent the depositions which need to be cleaned. Otherwise, it will cause an overheating condition. 


Now you know what causes the Noritz tankless water heater code 16 and how you can fix it. We strongly believe that the suggested outlines will be very effective to clear out the EC 16 of your Noritz water heater.

Plus, periodic maintenance is essential for your Noritz tankless water heater. If you maintain it properly, it will perform better overall and last longer. Yet, if you have any queries regarding this troubleshooting guide, leave a comment below.

About Phillip

Phillip is an HVAC guy & has convenient skills in the fireplace, heater, stove & other heating systems. He has been working and writing in this field for the last 5 years. He is really passionate about writing & share his expertise through his writing to help others. More about us.

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