Noritz NRCP Eco TOUGH Code Er66
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.
Also displayed as: 66, E66
Part replacementThe verdict
Replace a part
Same shape as Er65 and a different valve. Water hotter than the setting at low flow is the signature, because the blend that normally corrects it has stopped happening.
Typical cost: $200–$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 NRCP Eco TOUGH — not averaged across the brand.
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 exact series.
What you can safely check
- Note whether the problem is worst at a slowly running tap.
- Book a service call, and say it is the mixing valve, Er66.
Code Er66 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
One other Noritz NRCP Eco TOUGH code points 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: