Noritz tankless water heater code 66
Your series decides which reading applies. Across the 3 Noritz series documented here, code 66 is listed as bypass flow control valve fault (2 series) and bypass water servo fault (1 series). Find your series in the table below, where those readings route to a replacement part.
What code 66 means on each Noritz series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| EZ Series & NCC199CDV | Bypass water servo fault | Part replacement | $0–$700 |
| NCC199 & NRC111 | Bypass flow control valve fault | Part replacement | $0–$700 |
| NR98 & NR111 | Bypass flow control valve fault | Part replacement | $0–$700 |
Each row opens the full page for that generation. We hold manuals for EZ Series & NCC199CDV, NCC199 & NRC111 and NR98 & NR111, and each one gets its own reading of code 66 — what Noritz documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 3 series in four columns, which is enough to route you and not enough to explain anything. This is the Noritz wording behind each row, one entry per manual, so you can see where the 3 readings of code 66 agree and where they part company.
EZ Series & NCC199CDV — Bypass water servo fault
The bypass water servo is not functioning. This is the second motorised valve: it routes some water around the heat exchanger and blends it back in, which is what stops the outlet overshooting at low flow. Noritz's checks are the same as for code 65 — that the servo functions, and the connection at the valve — and the same power cycle to clear it.
NCC199 & NRC111 — 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.
NR98 & NR111 — 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.
Does it matter which Noritz you have?
EZ Series & NCC199CDV, NCC199 & NRC111 and NR98 & NR111 all route code 66 the same way: a replacement part, at $0–$700. That makes it one of the Noritz numbers you can act on before working out which unit you own.
Which Noritz do you have?
On the 3 series that report code 66, the model number on the rating label starts EZ, NCC, GQ, N and NRC — match yours against the 29 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
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 Noritz range.
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 Noritz range.
The same number on other brands
Code 66 is not a standard across the industry — every manufacturer publishes its own table. If your unit is not a Noritz, this number means something else entirely:
Parts, guides and symptoms behind code 66
Code 66 on these 3 Noritz series points at 1 guide, 1 part and 2 symptoms, each named by the manufacturer's own procedure for this code.