Noritz NRCP Code Er66
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.
Also displayed as: 66, E66
Part replacementThe verdict
Replace a part
Same shape as Er65 and a different valve. Expect water that runs hotter than the setting at low flow, 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 — not averaged across the brand.
Source: Noritz Service Manual — NRCP111-DV / NRCP98-DV (Rev. 09/19) (p. 62), 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 — that is the signature of a mixing valve fault.
- Book a service call, and say it is the mixing valve, Er66, not the control valve.
Code Er66 on other Noritz series
Code Er66 is a different fault on every other Noritz series that documents it, which is exactly why this page is written for the NRCP alone:
Don't confuse this with
3 other Noritz NRCP 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: