Noritz tankless water heater code Er66
Your series decides which reading applies. Across the 2 Noritz series documented here, code Er66 is listed as water mixing valve fault (1 series) and mixing valve fault (1 series). Find your series in the table below, where those readings route to a replacement part.
What code Er66 means on each Noritz series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| NRCP | Water mixing valve fault | Part replacement | $200–$700 |
| NRCP Eco TOUGH | Mixing valve fault | Part replacement | $200–$700 |
Each row opens the full page for that generation. We hold manuals for NRCP and NRCP Eco TOUGH, and each one gets its own reading of code Er66 — what Noritz documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 2 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 2 readings of code Er66 agree and where they part company.
NRCP — Water mixing valve fault
The mixing valve is not behaving. Noritz's remedy is one line — check the water mixing valve. This is the valve that blends unheated water back in to stop the outlet overshooting at low flow, which is why the fault shows up worst at a slowly running tap.
NRCP Eco TOUGH — Mixing valve fault
The mixing valve is not behaving. Noritz's remedy is one line — check the mixing valve. This is the valve that blends unheated water back in to stop the outlet overshooting at low flow, which is why the symptom is worst at a slowly running tap. Manual reset. Noritz calls this the mixing valve on the Eco TOUGH and the water mixing valve on the first generation, and only this table tells you it is a manual reset. On an NRCP111 or NRCP98 the same fault carries no reset guidance.
Does it matter which Noritz you have?
NRCP and NRCP Eco TOUGH all route code Er66 the same way: a replacement part, at $200–$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 2 series that report code Er66, the model number on the rating label starts NRCP — match yours against the 4 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Noritz Service Manual — NRCP111-DV / NRCP98-DV (Rev. 09/19) (p. 62), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Source: Noritz Service Manual — NRCP1112-DV / NRCP982-DV Eco TOUGH (Rev. 05/19) (p. 58), read Sep 2026 — the manufacturer's own documentation for this Noritz range.
Parts, guides and symptoms behind code Er66
Code Er66 on these 2 Noritz series points at 1 part and 2 symptoms, each named by the manufacturer's own procedure for this code.