Tankless Water Heater Shuts Down: Error Code 16

If your tankless water heater suddenly shuts down, first look at the control panel’s error code. If it’s a Noritz or Rheem tankless unit and it reads Error Code 16, it shut itself off for your safety.

Error code 16 means the unit suddenly reached a temperature far above the one you set. It automatically shuts itself completely off to prevent you from stepping into a scalding shower. A cold shower gets your attention safely.

Tankless water heater shuts down Error Code 16 prevents for safety

Error Code 16 means your Rheem or Noritz tankless water heater sensed temperature rising above what you set. So it shuts down for your safety.

What Causes a High Temperature Error Code 16 Shut Down?

  • #1 reason for Error Code 16 is scale build up. And scale builds up when mineral deposits are not routinely flushed from a tankless water heater’s heat exchanger.
  • #2 a clogged water filter
  • #3 low water pressure
  • #4 high gas pressure
  • #5 air flow restriction

Here’s What to Check if You See Error Code 16

How Long Ago Was Your Tankless Water Heater Flushed?

Since scale build up is by far the most likely cause, first ask yourself how long ago your tankless water heater was flushed. If it’s been a year or more, call us – 760-594-1226. We’re the leading water heater experts in this area and we’re here to help.

Or if you’re a do-it-yourselfer, read our post on how to flush a tankless water heater.

In our hard water area, mineral deposits accumulate quickly. That’s why many of our tankless customers choose to install a whole-house water softener and filtration system. It can not only extend the life of your water heater, but of all your water appliances.

tankless heat exchanger corroded because never flushed

This is what the inside of a tankless water heater looks like that has never been flushed. The mineral deposits eventually corroded the heat exchanger and caused the water heater to leak.

Is the Water Filter Dirty or Clogged?

If the filter is dirty, it can restrict the flow of water pressure and cause the water heater to overheat. That’s why your tankless water heater’s water filter needs to be cleaned out every six months to a year. We can do that as part of regular maintenance routine.

Do-it-yourselfer? Follow these steps to check and clean the water filter:

  • Turn off the power to the water heater.
  • Remove the lower panel.
  • Lift the handle of the cold water inlet to shut it off.
  • Shut off the hot water outlet by lifting the valve. (A bit of trapped water will come out.)
  • Locate the pressure relief valve connected to the drainpipe. A Noritz is usually on the side between the flush valves. A Rinnai is in the center. A Rheem (depending on the model) may not have a pressure relief valve. Release the valve. A little water may come out.
  • Find the filter plug and unscrew it. Remove the filter by sliding it off the plug. Wipe off debris with a rag or brush then run water through it to clean it.
  • Reattach the filter to the plug. Then hand screw the plug back into the unit.
  • Close up the lower panel.

Check Water Pressure

If your water pressure coming into the tankless unit is too low it can cause the temperature to rise above your set point too. Is the water pressure is low on all your outlets? Do your neighbors have the same issue? If it’s a problem only to your home, make sure your shutoff valve is completely open. If neighbors are impacted, it’s likely a temporary problem caused by your municipal water company. You can call them to find out.

If the Manifold Gas Pressures Are too High

The BTUs will be excessively high and cause the temperature to shoot up. You can use a digital manometer to check the gas pressure. Better yet, call us at 760-594-1226.

Is Anything Blocking the Air Flow?

A tankless water heater dissipates heat by blowing exhaust gas outside. If anything is blocking the vent, it can cause your tankless unit to overheat.

Call us! We are your local water heater experts.

We’ve been serving Fallbrook, Bonsall, Oceanside, Vista and Temecula for over 30 years. Water heaters is in our name for a reason. We’ve seen and fixed more water heater problems than any other plumber in the area. Plus we are locally owned and operated. In fact, I started out as a teenager helping in my dad’s plumbing business.

We are also the only plumber in the area to earn an all five-star customer satisfaction rating. We guarantee your satisfaction too.

Need more reasons to call us? Read why we’re the most affordable plumber in the area.

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