Noritz NR98 & NR111 Code 66
Bypass flow control valve fault. The bypass flow control valve is not functioning. Noritz heads the code "bypass flow control valve abnormality" and then, in the diagnosis column, asks you to check that the main water control valve is functioning — the manual's own wording, and worth knowing about before a technician arrives expecting one valve and finds the other named. The power has to be cycled to clear the code.
Also displayed as: F66
Part replacementThe verdict
Replace a part
Same shape as code 65 and the neighbouring valve. Expect water hotter than the setting at a slowly running tap, because the blend that normally corrects it has stopped happening.
Typical cost: $0–$700
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 NR98 & NR111 — not averaged across the brand.
Source: Noritz Service Manual — NR50 / NR66 / NR71 / NR98 / NCC199 / NRC111 / NR111 / NC380 (Rev. July 2011) (p. 56), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Cycle the power, which is Noritz's documented reset.
- If it returns, book a service call and mention that the manual's diagnosis line for this code names the main valve while the heading names the bypass.
Code 66 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:
Don't confuse this with
3 other Noritz NR98 & NR111 codes point at a valve too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: