Noritz EZ Series & NCC199CDV Code 13
External carbon monoxide alarm triggered. This is not a fault in the water heater. Code 13 means a carbon monoxide alarm wired to this appliance has gone off, and the heater has shut itself down in response. Noritz's checklist says what the alarm is reacting to: abnormal combustion, vent components that are not secure and fully connected, and exhaust leaking from the vent pipes. It also lists a cut CO alarm wire as a possible cause of the signal — but that is a diagnosis for afterwards, from outside the building, not a reason to assume it is a false alarm and stay put.
Also displayed as: F13
Emergency — stopThe verdict
Call a licensed plumber
There is nothing to price and nothing to check first. A CO alarm connected to this heater has triggered and the heater has stopped. Leave the building and call emergency services from outside it. The range below is for the vent or combustion work afterwards.
Typical cost: $0–$1,500
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.
Frequently asked questions
Noritz lists a cut alarm wire as a cause. Could it just be a wiring fault?
It could, and quite often is. But you cannot tell the difference from inside the building, and the cost of being wrong is measured in lives rather than dollars. Leave first, establish that it was the wiring second. Nobody has ever regretted evacuating over a faulty sensor.
Why does my heater have a CO alarm wired to it at all?
Some installations — particularly in confined spaces or where the venting arrangement warrants it — put a CO alarm on a circuit that shuts the appliance down when it triggers. It is a good thing to have. Code 13 is that interlock doing exactly what it was fitted to do.
Can I run the heater once the alarm stops?
Not until a professional has been through Noritz's list — abnormal combustion, vent components secure and fully connected, and exhaust leaking from vent pipes. An alarm that stops sounding means the air cleared, not that the source is gone.