Noritz NCC199 & NRC111 Code 59
Heat exchanger flow fault. Noritz puts scale first in the remedy for this one: check for scale build-up in the heat exchanger, then abnormal combustion, then the flue for blockage or obstruction, then that the flame ignites all the way across the burner. It is the closest thing this series has to a dedicated descaling code, and Noritz notes that it does not appear in the manual's own troubleshooting flowchart.
Also displayed as: F59
DIY fixThe verdict
Descale the unit
Start with the flush, because Noritz does. A scaled heat exchanger restricts flow, which is what this code measures, and a flush is a kit and an afternoon against a heat exchanger that is most of the value of the appliance. If a genuine flush does not clear it, the remaining causes are combustion and the flue, and those are not yours.
Typical cost: $40–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NCC199 & NRC111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 55), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Flush the heat exchanger — our descaling guide covers it end to end.
- Check the vent terminal outside while you are at it, since the flue is Noritz's third cause.
- If the code survives a proper flush, book a service call rather than flushing again.
- Afterwards, work out your water hardness and set a flushing interval from it.
Frequently asked questions
Does this series have a scale warning like the C1 code on other Noritz models?
No. The NRC661 range counts hours and prompts you with C1 through C4 before locking out at CF; this table has none of that. Code 59 is the appliance noticing the consequence — flow through a restricted heat exchanger — rather than counting down to it. By the time you see 59, the scale is already doing work.
Code 59 on other Noritz series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: