Noritz NCC199 & NRC111 Code 66
Bypass flow control valve fault. The bypass flow control valve is not functioning. Same two checks as code 65 and the same power cycle to clear it. This is the second motorised valve: it routes water around the heat exchanger and blends it back, which is what stops the outlet overshooting at low flow.
Also displayed as: F66
Part replacementThe verdict
Replace a part
Same shape as code 65, different 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 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
- Cycle the power, which is Noritz's documented reset.
- If it returns, book a service call and say it is the bypass valve, code 66, not the main one.
Code 66 on other Noritz series
Noritz keeps the same fault name for code 66 on some series and not others. Check the one that matches your rating label:
Don't confuse this with
2 other Noritz NCC199 & NRC111 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: