Noritz EZ Series & NCC199CDV Code 10
Combustion fault recorded in history. A combustion abnormality the unit did not stop for. Noritz notes this one as "only memorized in error code history", which means you will normally find it by reading the history rather than by seeing it on the controller. The checklist is the full combustion set — air supply vent and exhaust vent for blockage, gas supply pressure checked by a professional, the condensate drain line clogged or frozen, the drain pipe sloping down, and the dip switch settings on the circuit board.
Also displayed as: F10
Call a proThe verdict
Call a licensed plumber
A stored combustion fault is worth acting on precisely because the unit did not stop for it. Two of Noritz's causes are yours to look at for nothing — the vent terminal outside and the condensate line — and finding one of those explains it cheaply.
Typical cost: $0–$900
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.
- Check the vent terminal and air inlet outside for snow, leaves, a nest or anything built against them.
- Follow the condensate drain line and check it is clear, unfrozen, and sloping downhill the whole way.
- If both are clear, book a licensed professional — the rest of the list is gas pressure and board settings.
Frequently asked questions
I found a 10 in the history but the unit works. Do I ignore it?
No, but you do not need to panic either. Noritz records this code without shutting the unit down, which means the appliance saw combustion go out of range and recover. The cheap causes — a partly blocked terminal, a condensate line starting to freeze — are the ones you can rule out yourself before paying anyone.
Code 10 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: