How often does a Noritz need descaling to avoid code 16?

With hard water, about every 12 months. With softer water, less often, according to your manual.

Noritz Error Code 16: Water Too Hot, Usually Scale

Code 16 is the Noritz overheat warning for the water leaving the heater. When the temperature spikes, the heater restricts its operation.

Why scale causes code 16

Scale inside the heat exchanger acts as insulation. The unit has to fire harder to heat the water, and temperatures inside can overshoot. That is why code 16 is so common in hard water areas.

What to do

Descale the heat exchanger. Follow the Noritz procedure in your manual, or our guide to descale a tankless water heater.
Clean the inlet water filter.
Reset the unit and watch whether the code returns.

Prevent it

Descale every 12 months with hard water. A water softener or scale-prevention filter on the cold supply slows scale buildup.

When to call a contractor

Call a licensed contractor if code 16 returns after you have descaled the heat exchanger and cleaned the inlet filter, or if you are not comfortable descaling the unit yourself. A code that keeps returning means the cause has not been found, and the unit needs a professional inspection.

Other Noritz codes

Code	Meaning
10	Combustion abnormality (warning)
11	Ignition failure
12	Flame loss
13	Optional CO alarm device fault
14	Thermal fuse blown (severe overheat)
16	Outlet water temperature spiked too high
20	High limit switch tripped
29	Condensate drain problem (condensing models)
67	Air gas mixer (AGM) abnormality
71	Gas valve circuit abnormality
90	Combustion abnormality
92	Neutralizer near end of life (first warning)
93	Neutralizer at end of life

Noritz error code 16: outlet water too hot, causes and fixes