Noritz EZ Series & NCC199CDV Code 15
Abnormally high input temperature. The water arriving at the primary heat exchanger is hotter than it should be. Noritz checks the resistance of the primary heat exchanger inlet thermistor and then asks you to check the gas type. This code does not exist on the NRC table, because that series does not have a separate inlet thermistor on the heat exchanger to report it.
Also displayed as: F15
Call a proThe verdict
Call a licensed plumber
Two very different causes: a sensor reading wrongly, which is cheap, or the appliance genuinely being fed hot water — commonly a recirculation loop or a solar pre-heat plumbed in without the unit being told about it. Noritz putting gas type on the list makes it a professional call either way.
Typical cost: $150–$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 EZ Series & NCC199CDV — not averaged across the brand.
Source: Noritz Service Manual — NRC663 FSV, EZ98DV, EZ111DV, NCC199CDV (Rev. Oct 2017) (p. 32), read Sep 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Tell the technician whether there is a recirculation loop, a solar pre-heat or a second heat source upstream of this unit.
- Note whether the unit was ever converted between natural gas and propane.
- Book a licensed professional.